The main purpose of this series is patch 5, which can avoid delaying flips for a frame in some cases. It depends on patch 4 to prevent flips from taking effect too early, which in turn depends on the core DRM patch 2.
Patches 1 & 3 are cleanups I noticed while working on the other patches.
Mario, it would be great if you could run these through your rigorous vblank testing.
[PATCH 1/5] drm: Only handle _DRM_VBLANK_NEXTONMISS once [PATCH 2/5] drm: Keep track of last vblank sequence waited for [PATCH 3/5] drm/amdgpu: Unpin BO if we can't get fences in [PATCH 4/5] drm/amdgpu: Wait for end of last waited-for vblank before [PATCH 5/5] drm/amdgpu: Set MASTER_UPDATE_MODE to 0 again
From: Michel Dänzer michel.daenzer@amd.com
Consolidate the _DRM_VBLANK_NEXTONMISS handling between drm_wait_vblank and drm_queue_vblank_event.
This is a cleanup spotted while working on the next change.
(The way it was previously handled could also theoretically result in drm_queue_vblank_event unnecessarily bumping vblwait->request.sequence, if the vblank counter happened to increment between the drm_vblank_count(_and_time) calls in each function, but that's unlikely)
Signed-off-by: Michel Dänzer michel.daenzer@amd.com --- drivers/gpu/drm/drm_irq.c | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 3c1a6f1..39ea4fc 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1685,12 +1685,6 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
seq = drm_vblank_count_and_time(dev, pipe, &now);
- if ((vblwait->request.type & _DRM_VBLANK_NEXTONMISS) && - (seq - vblwait->request.sequence) <= (1 << 23)) { - vblwait->request.sequence = seq + 1; - vblwait->reply.sequence = vblwait->request.sequence; - } - DRM_DEBUG("event on vblank count %d, current %d, crtc %u\n", vblwait->request.sequence, seq, pipe);
@@ -1787,6 +1781,11 @@ int drm_wait_vblank(struct drm_device *dev, void *data, goto done; }
+ if ((flags & _DRM_VBLANK_NEXTONMISS) && + (seq - vblwait->request.sequence) <= (1 << 23)) { + vblwait->request.sequence = seq + 1; + } + if (flags & _DRM_VBLANK_EVENT) { /* must hold on to the vblank ref until the event fires * drm_vblank_put will be called asynchronously @@ -1794,11 +1793,6 @@ int drm_wait_vblank(struct drm_device *dev, void *data, return drm_queue_vblank_event(dev, pipe, vblwait, file_priv); }
- if ((flags & _DRM_VBLANK_NEXTONMISS) && - (seq - vblwait->request.sequence) <= (1<<23)) { - vblwait->request.sequence = seq + 1; - } - DRM_DEBUG("waiting on vblank count %d, crtc %u\n", vblwait->request.sequence, pipe); vblank->last_wait = vblwait->request.sequence;
From: Michel Dänzer michel.daenzer@amd.com
The per-device tracking hasn't been used since commit dafffda0 ("drm/info: Remove unused code").
The per-file-descriptor tracking will be used by a following amdgpu driver change.
Note that last_vblank_wait is only updated when the corresponding wait completes, and is set to the vblank seqno waited for, not the current one when the wait completes.
Signed-off-by: Michel Dänzer michel.daenzer@amd.com --- drivers/gpu/drm/drm_fops.c | 8 ++++++++ drivers/gpu/drm/drm_irq.c | 18 +++++++++++++++++- include/drm/drmP.h | 4 +++- 3 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index 7af7f8b..1f52f02 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -256,6 +256,13 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor) priv->pid = get_pid(task_pid(current)); priv->minor = minor;
+ if (drm_is_primary_client(priv)) { + priv->num_crtcs = dev->num_crtcs; + priv->last_vblank_wait = kcalloc(priv->num_crtcs, + sizeof(*priv->last_vblank_wait), + GFP_KERNEL); + } + /* for compatibility root is always authenticated */ priv->authenticated = capable(CAP_SYS_ADMIN); priv->lock_count = 0; @@ -530,6 +537,7 @@ int drm_release(struct inode *inode, struct file *filp) WARN_ON(!list_empty(&file_priv->event_list));
put_pid(file_priv->pid); + kfree(file_priv->last_vblank_wait); kfree(file_priv);
/* ======================================================== diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 39ea4fc..62845f4 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -77,6 +77,15 @@ MODULE_PARM_DESC(vblankoffdelay, "Delay until vblank irq auto-disable [msecs] (0 MODULE_PARM_DESC(timestamp_precision_usec, "Max. error on timestamps [usecs]"); MODULE_PARM_DESC(timestamp_monotonic, "Use monotonic timestamps");
+/* Keep track of the latest seqno waited for by this file descriptor */ +static void update_last_vblank_wait(struct drm_file *file_priv, unsigned pipe, + u32 seq) +{ + if (pipe < file_priv->num_crtcs && + (int)(seq - file_priv->last_vblank_wait[pipe]) > 0) + file_priv->last_vblank_wait[pipe] = seq; +} + static void store_vblank(struct drm_device *dev, unsigned int pipe, u32 vblank_count_inc, struct timeval *t_vblank, u32 last) @@ -1694,6 +1703,9 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe, e->event.sequence = vblwait->request.sequence; if ((seq - vblwait->request.sequence) <= (1 << 23)) { drm_vblank_put(dev, pipe); + + update_last_vblank_wait(file_priv, pipe, + vblwait->request.sequence); send_vblank_event(dev, e, seq, &now); vblwait->reply.sequence = seq; } else { @@ -1795,7 +1807,6 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
DRM_DEBUG("waiting on vblank count %d, crtc %u\n", vblwait->request.sequence, pipe); - vblank->last_wait = vblwait->request.sequence; DRM_WAIT_ON(ret, vblank->queue, 3 * HZ, (((drm_vblank_count(dev, pipe) - vblwait->request.sequence) <= (1 << 23)) || @@ -1805,6 +1816,9 @@ int drm_wait_vblank(struct drm_device *dev, void *data, if (ret != -EINTR) { struct timeval now;
+ update_last_vblank_wait(file_priv, pipe, + vblwait->request.sequence); + vblwait->reply.sequence = drm_vblank_count_and_time(dev, pipe, &now); vblwait->reply.tval_sec = now.tv_sec; vblwait->reply.tval_usec = now.tv_usec; @@ -1841,6 +1855,8 @@ static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
list_del(&e->base.link); drm_vblank_put(dev, pipe); + update_last_vblank_wait(e->base.file_priv, pipe, + e->event.sequence); send_vblank_event(dev, e, seq, &now); }
diff --git a/include/drm/drmP.h b/include/drm/drmP.h index 360b2a7..d7c95b6 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -354,6 +354,9 @@ struct drm_file { struct mutex event_read_lock;
struct drm_prime_file_private prime; + + unsigned num_crtcs; + u32 *last_vblank_wait; /* Last vblank seqno waited per CRTC */ };
/** @@ -733,7 +736,6 @@ struct drm_vblank_crtc { atomic_t refcount; /* number of users of vblank interruptsper crtc */ u32 last; /* protected by dev->vbl_lock, used */ /* for wraparound handling */ - u32 last_wait; /* Last vblank seqno waited per CRTC */ unsigned int inmodeset; /* Display driver is setting mode */ unsigned int pipe; /* crtc index */ int framedur_ns; /* frame/field duration in ns */
From: Michel Dänzer michel.daenzer@amd.com
If reservation_object_get_fences_rcu failed, we'd previously go directly to the cleanup label, so we'd leave the BO pinned.
While we're at it, remove two amdgpu_bo_unreserve calls in favour of two new labels.
Signed-off-by: Michel Dänzer michel.daenzer@amd.com --- drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c index 7268030..de95ea7 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c @@ -220,19 +220,17 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc,
r = amdgpu_bo_pin_restricted(new_rbo, AMDGPU_GEM_DOMAIN_VRAM, 0, 0, &base); if (unlikely(r != 0)) { - amdgpu_bo_unreserve(new_rbo); r = -EINVAL; DRM_ERROR("failed to pin new rbo buffer before flip\n"); - goto cleanup; + goto unreserve; }
r = reservation_object_get_fences_rcu(new_rbo->tbo.resv, &work->excl, &work->shared_count, &work->shared); if (unlikely(r != 0)) { - amdgpu_bo_unreserve(new_rbo); DRM_ERROR("failed to get fences for buffer\n"); - goto cleanup; + goto unpin; }
amdgpu_bo_get_tiling_flags(new_rbo, &tiling_flags); @@ -275,9 +273,11 @@ pflip_cleanup: DRM_ERROR("failed to reserve new rbo in error path\n"); goto cleanup; } +unpin: if (unlikely(amdgpu_bo_unpin(new_rbo) != 0)) { DRM_ERROR("failed to unpin new rbo in error path\n"); } +unreserve: amdgpu_bo_unreserve(new_rbo);
cleanup:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
Signed-off-by: Michel Dänzer michel.daenzer@amd.com --- drivers/gpu/drm/amd/amdgpu/amdgpu.h | 3 ++- drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 34 +++++++++++++++++++++++++---- 2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h index 992f00b..7b53967 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h @@ -712,10 +712,11 @@ void amdgpu_doorbell_get_kfd_info(struct amdgpu_device *adev, */
struct amdgpu_flip_work { - struct work_struct flip_work; + struct delayed_work flip_work; struct work_struct unpin_work; struct amdgpu_device *adev; int crtc_id; + u32 avoid_vblank; uint64_t base; struct drm_pending_vblank_event *event; struct amdgpu_bo *old_rbo; diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c index de95ea7..a9f7851 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c @@ -41,7 +41,7 @@ static void amdgpu_flip_callback(struct fence *f, struct fence_cb *cb) container_of(cb, struct amdgpu_flip_work, cb);
fence_put(f); - schedule_work(&work->flip_work); + schedule_work(&work->flip_work.work); }
static bool amdgpu_flip_handle_fence(struct amdgpu_flip_work *work, @@ -63,8 +63,10 @@ static bool amdgpu_flip_handle_fence(struct amdgpu_flip_work *work,
static void amdgpu_flip_work_func(struct work_struct *__work) { + struct delayed_work *delayed_work = + container_of(__work, struct delayed_work, work); struct amdgpu_flip_work *work = - container_of(__work, struct amdgpu_flip_work, flip_work); + container_of(delayed_work, struct amdgpu_flip_work, flip_work); struct amdgpu_device *adev = work->adev; struct amdgpu_crtc *amdgpuCrtc = adev->mode_info.crtcs[work->crtc_id];
@@ -81,6 +83,19 @@ static void amdgpu_flip_work_func(struct work_struct *__work) if (amdgpu_flip_handle_fence(work, &work->shared[i])) return;
+ /* Wait until we're out of the last waited-for vertical blank + * period + */ + if (amdgpuCrtc->enabled && + drm_crtc_vblank_count(crtc) == work->avoid_vblank && + (amdgpu_get_crtc_scanoutpos(adev->ddev, work->crtc_id, 0, + &vpos, &hpos, NULL, NULL, + &crtc->hwmode) + & DRM_SCANOUTPOS_IN_VBLANK)) { + schedule_delayed_work(&work->flip_work, usecs_to_jiffies(1000)); + return; + } + /* We borrow the event spin lock for protecting flip_status */ spin_lock_irqsave(&crtc->dev->event_lock, flags);
@@ -175,6 +190,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, uint32_t page_flip_flags) { struct drm_device *dev = crtc->dev; + struct drm_file *file_priv = event->base.file_priv; struct amdgpu_device *adev = dev->dev_private; struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(crtc); struct amdgpu_framebuffer *old_amdgpu_fb; @@ -191,7 +207,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, if (work == NULL) return -ENOMEM;
- INIT_WORK(&work->flip_work, amdgpu_flip_work_func); + INIT_DELAYED_WORK(&work->flip_work, amdgpu_flip_work_func); INIT_WORK(&work->unpin_work, amdgpu_unpin_work_func);
work->event = event; @@ -244,6 +260,16 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, goto pflip_cleanup; }
+ /* If this file descriptor has waited for the current vblank period, + * do not program the flip during this vblank period + */ + if (amdgpu_crtc->crtc_id < file_priv->num_crtcs) + work->avoid_vblank = + file_priv->last_vblank_wait[amdgpu_crtc->crtc_id]; + + if (!work->avoid_vblank) + work->avoid_vblank = drm_crtc_vblank_count(crtc) - 1; + /* we borrow the event spin lock for protecting flip_wrok */ spin_lock_irqsave(&crtc->dev->event_lock, flags); if (amdgpu_crtc->pflip_status != AMDGPU_FLIP_NONE) { @@ -262,7 +288,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, /* update crtc fb */ crtc->primary->fb = fb; spin_unlock_irqrestore(&crtc->dev->event_lock, flags); - amdgpu_flip_work_func(&work->flip_work); + amdgpu_flip_work_func(&work->flip_work.work); return 0;
vblank_cleanup:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
That way it would be all nicely contained to amdgpu, and not leaking into the core. -Daniel
Signed-off-by: Michel Dänzer michel.daenzer@amd.com
drivers/gpu/drm/amd/amdgpu/amdgpu.h | 3 ++- drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 34 +++++++++++++++++++++++++---- 2 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h index 992f00b..7b53967 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h @@ -712,10 +712,11 @@ void amdgpu_doorbell_get_kfd_info(struct amdgpu_device *adev, */
struct amdgpu_flip_work {
- struct work_struct flip_work;
- struct delayed_work flip_work; struct work_struct unpin_work; struct amdgpu_device *adev; int crtc_id;
- u32 avoid_vblank; uint64_t base; struct drm_pending_vblank_event *event; struct amdgpu_bo *old_rbo;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c index de95ea7..a9f7851 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c @@ -41,7 +41,7 @@ static void amdgpu_flip_callback(struct fence *f, struct fence_cb *cb) container_of(cb, struct amdgpu_flip_work, cb);
fence_put(f);
- schedule_work(&work->flip_work);
- schedule_work(&work->flip_work.work);
}
static bool amdgpu_flip_handle_fence(struct amdgpu_flip_work *work, @@ -63,8 +63,10 @@ static bool amdgpu_flip_handle_fence(struct amdgpu_flip_work *work,
static void amdgpu_flip_work_func(struct work_struct *__work) {
- struct delayed_work *delayed_work =
container_of(__work, struct delayed_work, work);
container_of(__work, struct amdgpu_flip_work, flip_work);
container_of(delayed_work, struct amdgpu_flip_work, flip_work);@@ -81,6 +83,19 @@ static void amdgpu_flip_work_func(struct work_struct *__work) if (amdgpu_flip_handle_fence(work, &work->shared[i])) return;
- /* Wait until we're out of the last waited-for vertical blank
* period*/- if (amdgpuCrtc->enabled &&
drm_crtc_vblank_count(crtc) == work->avoid_vblank &&(amdgpu_get_crtc_scanoutpos(adev->ddev, work->crtc_id, 0,&vpos, &hpos, NULL, NULL,&crtc->hwmode)& DRM_SCANOUTPOS_IN_VBLANK)) {schedule_delayed_work(&work->flip_work, usecs_to_jiffies(1000));return;- }
- /* We borrow the event spin lock for protecting flip_status */ spin_lock_irqsave(&crtc->dev->event_lock, flags);
@@ -175,6 +190,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, uint32_t page_flip_flags) { struct drm_device *dev = crtc->dev;
- struct drm_file *file_priv = event->base.file_priv; struct amdgpu_device *adev = dev->dev_private; struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(crtc); struct amdgpu_framebuffer *old_amdgpu_fb;
@@ -191,7 +207,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, if (work == NULL) return -ENOMEM;
- INIT_WORK(&work->flip_work, amdgpu_flip_work_func);
INIT_DELAYED_WORK(&work->flip_work, amdgpu_flip_work_func); INIT_WORK(&work->unpin_work, amdgpu_unpin_work_func);
work->event = event;
@@ -244,6 +260,16 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, goto pflip_cleanup; }
- /* If this file descriptor has waited for the current vblank period,
* do not program the flip during this vblank period*/- if (amdgpu_crtc->crtc_id < file_priv->num_crtcs)
work->avoid_vblank =file_priv->last_vblank_wait[amdgpu_crtc->crtc_id];- if (!work->avoid_vblank)
work->avoid_vblank = drm_crtc_vblank_count(crtc) - 1;- /* we borrow the event spin lock for protecting flip_wrok */ spin_lock_irqsave(&crtc->dev->event_lock, flags); if (amdgpu_crtc->pflip_status != AMDGPU_FLIP_NONE) {
@@ -262,7 +288,7 @@ int amdgpu_crtc_page_flip(struct drm_crtc *crtc, /* update crtc fb */ crtc->primary->fb = fb; spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
- amdgpu_flip_work_func(&work->flip_work);
- amdgpu_flip_work_func(&work->flip_work.work); return 0;
vblank_cleanup:
2.8.1
dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are: - The timestamp for vblank event needs to agree with whatever oml_sync requries. - The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip. - The event needs to be after the old buffers are not longer used and can be reused for rendering. - There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work - that kind of precision is why we have a separate timestamp.
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, no single-use driver oddity in the core, and you still can page_flip as late as you want without forcing a delay to the next vblank if your already past the start of vblank. And since you have high-precision timestamp support the vblank core will fudge the timestamp as needed.
Ofc this assumes that amd hw has a vblank_end irq, but most desktop hw seems to have that (didn't check tbh whether amd has it). So all that's needed I think is to enable the vblank_end irq (in lockstep with the start one) and move drm_handle_vblank() from its current place to that new irq. -Daniel
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
Yup, mixed that up.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
Most hw just seems to give you a vblank interrupt somewhere in the vblank are, or sometimes even slightly before that. Also there's scheduling jitter.
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about. The above few rules are what generic userspace (afaik at least) cares about, and what therefore drivers should implement. Note that at least to my knowledge absolutely nothing cares when exactly in the vblank the interrupt fires, and the event gets delivered. We even moved that around in the i915 driver iirc, exactly because you could squeeze in a page-flip like you can here on radeon. -Daniel
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote:
From: Michel Dänzer michel.daenzer@amd.com
If userspace wants a page flip to take effect during vblank sequence n, it has to wait for vblank seqno n-1 before calling the DRM_IOCTL_MODE_PAGE_FLIP ioctl.
This change makes sure that we do not program the flip to the hardware before the end of vblank seqno n-1 in this case, to prevent the flip from taking effect too early.
On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called during vblank, but userspace didn't wait for the current vblank seqno before, this change would still allow the flip to be programmed during the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
Yup, mixed that up.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
Most hw just seems to give you a vblank interrupt somewhere in the vblank are, or sometimes even slightly before that.
Our hardware tends to trigger the vblank interrupt early, but it's still useful in that drawing operations submitted after it cannot affect the previously scanned out frame.
Also there's scheduling jitter.
Sure, but there's a big difference between "no guarantee that we're still in vblank" vs "guarantee that we're no longer in vblank".
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote:
On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote: > From: Michel Dänzer michel.daenzer@amd.com > > If userspace wants a page flip to take effect during vblank sequence n, > it has to wait for vblank seqno n-1 before calling the > DRM_IOCTL_MODE_PAGE_FLIP ioctl. > > This change makes sure that we do not program the flip to the hardware > before the end of vblank seqno n-1 in this case, to prevent the flip > from taking effect too early. > > On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called > during vblank, but userspace didn't wait for the current vblank seqno > before, this change would still allow the flip to be programmed during > the current vblank seqno.
This just sounds like you're sending vblank events out a bit too early. And watching vblank waits that userspace does works, but it's fragile, add-hoc and I don't really jump in joy about adding that to the vblank core. Is there no way you can adjust sending out the vblank events similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
Yup, mixed that up.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
Most hw just seems to give you a vblank interrupt somewhere in the vblank are, or sometimes even slightly before that.
Our hardware tends to trigger the vblank interrupt early, but it's still useful in that drawing operations submitted after it cannot affect the previously scanned out frame.
Also there's scheduling jitter.
Sure, but there's a big difference between "no guarantee that we're still in vblank" vs "guarantee that we're no longer in vblank".
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati? I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever. Afaik others don't use it like that, at least not on intel. Weston has some hacks to use vblank waits for plane flips, but that's all disabled code because it just doesn't work - you need full atomic.
Anyway, I still don't like adding hacks to drm core like this for single-use in just one driver. drm_irq.c is already really complex and suffering badly from this, and we're pretty close to always accidentally breaking something when touching it. How bad would it really be to just always delay the page_flip past vblank? Userspace can still use async flips for lower latency.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag). It would also neatly fit into atomic plans, since we want to implement that (so that everyone has a benchmarking/low-latency mode, without hw support for async flips on all planes). And it wouldn't need special tracking code in drm_irq.c, making me happy. Thoughts? -Daniel
On 14.06.2016 14:53, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote:
On 10.06.2016 23:43, Daniel Vetter wrote: > On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote: >> From: Michel Dänzer michel.daenzer@amd.com >> >> If userspace wants a page flip to take effect during vblank sequence n, >> it has to wait for vblank seqno n-1 before calling the >> DRM_IOCTL_MODE_PAGE_FLIP ioctl. >> >> This change makes sure that we do not program the flip to the hardware >> before the end of vblank seqno n-1 in this case, to prevent the flip >> from taking effect too early. >> >> On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called >> during vblank, but userspace didn't wait for the current vblank seqno >> before, this change would still allow the flip to be programmed during >> the current vblank seqno. > > This just sounds like you're sending vblank events out a bit too early. > And watching vblank waits that userspace does works, but it's fragile, > add-hoc and I don't really jump in joy about adding that to the vblank > core. Is there no way you can adjust sending out the vblank events > similarly, to make sure userspace can never sneak in a pageflip too early?
What you call "too early" is actually "during the vertical blank period waited for". IMHO only notifying userspace of a vertical blank period when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
Yup, mixed that up.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
Most hw just seems to give you a vblank interrupt somewhere in the vblank are, or sometimes even slightly before that.
Our hardware tends to trigger the vblank interrupt early, but it's still useful in that drawing operations submitted after it cannot affect the previously scanned out frame.
Also there's scheduling jitter.
Sure, but there's a big difference between "no guarantee that we're still in vblank" vs "guarantee that we're no longer in vblank".
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati?
Yes. With DRI3/Present, it's driver independent code in xserver/present/. With DRI2, it's theoretically up to the DDX driver, but all drivers seem to have basically the same logic; the modesetting driver certainly does.
I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever.
Please don't try to single out our drivers, it seems like rather your driver is the odd man out in this case.
Afaik others don't use it like that, at least not on intel.
UXA has the same DRI2 logic, not sure about SNA.
Anyway, I still don't like adding hacks to drm core like this for single-use in just one driver.
The driver changes will be ported to radeon of course, and why couldn't it be used by other drivers for the same purpose?
drm_irq.c is already really complex and suffering badly from this, and we're pretty close to always accidentally breaking something when touching it.
I just don't see how my change makes this any worse.
How bad would it really be to just always delay the page_flip past vblank?
In the variable refresh rate case it could be pretty bad, basically dropping to the minimum refresh rate.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag).
That would be an inferior solution compared to my series, e.g.: If userspace calls DRM_IOCTL_MODE_PAGE_FLIP before the target vblank seqno is reached, it cannot use the new flag, otherwise the flip might take effect too early. However, if we are then already in the target vblank period when the fences have signalled and we are ready to program the flip, we have to wait for the end of vblank first, and the flip will be delayed by one frame.
If we're going to change the userspace interface, it would be better to re-purpose the reserved field of struct drm_mode_crtc_page_flip for explicitly specifying the target vblank seqno (via a new cap and flag). Then the kernel and userspace would no longer need to second-guess each other.
But even if we take that route, this series would be desirable for getting us most of the way there for existing userspace.
On Tue, Jun 14, 2016 at 04:25:28PM +0900, Michel Dänzer wrote:
On 14.06.2016 14:53, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 10:54:37AM +0900, Michel Dänzer wrote: > On 10.06.2016 23:43, Daniel Vetter wrote: >> On Fri, Jun 10, 2016 at 05:57:12PM +0900, Michel Dänzer wrote: >>> From: Michel Dänzer michel.daenzer@amd.com >>> >>> If userspace wants a page flip to take effect during vblank sequence n, >>> it has to wait for vblank seqno n-1 before calling the >>> DRM_IOCTL_MODE_PAGE_FLIP ioctl. >>> >>> This change makes sure that we do not program the flip to the hardware >>> before the end of vblank seqno n-1 in this case, to prevent the flip >>> from taking effect too early. >>> >>> On the other hand, if the DRM_IOCTL_MODE_PAGE_FLIP ioctl is called >>> during vblank, but userspace didn't wait for the current vblank seqno >>> before, this change would still allow the flip to be programmed during >>> the current vblank seqno. >> >> This just sounds like you're sending vblank events out a bit too early. >> And watching vblank waits that userspace does works, but it's fragile, >> add-hoc and I don't really jump in joy about adding that to the vblank >> core. Is there no way you can adjust sending out the vblank events >> similarly, to make sure userspace can never sneak in a pageflip too early? > > What you call "too early" is actually "during the vertical blank period > waited for". IMHO only notifying userspace of a vertical blank period > when it's already over would defeat the purpose.
Afaiui the rules are:
- The timestamp for vblank event needs to agree with whatever oml_sync requries.
- The event delivery itself needs to be consistent with what page_flip takes, i.e. if userspace sees an event and immediately issues a page_flip then it should not be able to hit the same vblank with that pageflip.
- The event needs to be after the old buffers are not longer used and can be reused for rendering.
That's only relevant for DRM_IOCTL_MODE_PAGE_FLIP, not DRM_IOCTL_WAIT_VBLANK.
Yup, mixed that up.
- There's no requirement at all that the event gets delivered at a specific point in the vblank, hardware is too different for that to work
As the name implies, the purpose of DRM_IOCTL_WAIT_VBLANK is to wait for a vertical blank period. If that doesn't work as intended with some hardware, that's tough luck but not really my problem. :)
- that kind of precision is why we have a separate timestamp.
I'm afraid this last item gives away that you're relatively new to this code. ;) The timestamp was originally literally just the current gettimeofday when the wait finished (the original DRM_IOCTL_WAIT_VBLANK ioctl didn't have any asynchronous notification functionality). It was relatively recently that Mario changed the timestamp to correspond to the end of the vertical blank period / start of scanout of the next frame, presumably due to your first rule above.
Most hw just seems to give you a vblank interrupt somewhere in the vblank are, or sometimes even slightly before that.
Our hardware tends to trigger the vblank interrupt early, but it's still useful in that drawing operations submitted after it cannot affect the previously scanned out frame.
Also there's scheduling jitter.
Sure, but there's a big difference between "no guarantee that we're still in vblank" vs "guarantee that we're no longer in vblank".
I assume you're goal is to not delay page_flips unecessarily, without breaking requirement 2 here. Imo a simpler fix would be to delay the vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati?
Yes. With DRI3/Present, it's driver independent code in xserver/present/. With DRI2, it's theoretically up to the DDX driver, but all drivers seem to have basically the same logic; the modesetting driver certainly does.
Hm, didn't know that everyone does that. Seemed to silly an idea to waste all that gpu bandwidth by waiting for vblank ...
I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever.
Please don't try to single out our drivers, it seems like rather your driver is the odd man out in this case.
Hm, why/where is i915 special? It sounds like it's very much not, it's just that normal page_flips (i.e. neither async nor variable refresh rate) get committed atomically by the hw at the exact same time the vblank irq fires. And if you look at the metric pile of atomic drivers we now have, they at least seem to all work like that. Afaik amd hw seems to be the exception with being able to make a flip still happen after the vblank fired. I didn't check nouveau, maybe that one is similar.
Afaik others don't use it like that, at least not on intel.
UXA has the same DRI2 logic, not sure about SNA.
Anyway, I still don't like adding hacks to drm core like this for single-use in just one driver.
The driver changes will be ported to radeon of course, and why couldn't it be used by other drivers for the same purpose?
Because other drivers work already, see above. At least all the atomic drivers will work like that, or at least seem to be written to work like that. So afaics it's amd drivers only.
drm_irq.c is already really complex and suffering badly from this, and we're pretty close to always accidentally breaking something when touching it.
I just don't see how my change makes this any worse.
It's death by a thousand cuts. Of course none of the individual ones are bad alone.
How bad would it really be to just always delay the page_flip past vblank?
In the variable refresh rate case it could be pretty bad, basically dropping to the minimum refresh rate.
Variable refresh rate is entirely undefined right now in kms. We probably need an entirely new set of flags to make that work smoothly. And I think even for variable rate refresh you want the current vblank stuff to tick as regularly as possible. And then your page_flip (without special flags would only need to make sure it's not faster than that). Variable refresh rate page_flips probably need a special flag, maybe even the same dont-tear-but-flip-asap flag.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag).
That would be an inferior solution compared to my series, e.g.: If userspace calls DRM_IOCTL_MODE_PAGE_FLIP before the target vblank seqno is reached, it cannot use the new flag, otherwise the flip might take effect too early. However, if we are then already in the target vblank period when the fences have signalled and we are ready to program the flip, we have to wait for the end of vblank first, and the flip will be delayed by one frame.
If we're going to change the userspace interface, it would be better to re-purpose the reserved field of struct drm_mode_crtc_page_flip for explicitly specifying the target vblank seqno (via a new cap and flag). Then the kernel and userspace would no longer need to second-guess each other.
But even if we take that route, this series would be desirable for getting us most of the way there for existing userspace.
Well that's what I mean. You'r patches here shoehorn what you want into existing api, trying to second-guess userspaces intentions inferred from what it does. Ime that tends to end in trouble. It would be much better to have a clear uabi for this. And my flag was just a suggestion.
I just had a discussion on irc with Dave about another topic were Dave complained about some of the inferred abi rules SNA uses (entirely differently, in probe code). And I thought it was a nice idea, since hey it works and its easier. But really it's not, since in the end kms is supposed to be somewhat generic. And usually your nice idea for inferring behaviour then tends to break down somewhere. At least I think the generic kms rules are:
- vblank events fire at lockstep (not everyone gets this right, but you end up with either lagging desktop or 100% cpu usuage on weston if you don't). Which also means for variable refresh rate you need to keep this vblank running at full refresh rate (which is annoying, but just means we need a flag for vblank waits). - pageflip immediately after a vblank wait needs to hit the next vblank. - pageflip in a loop needs to result in at most 1 flip per vblank, and if you're too fast then the kernel should return -EBUSY. Latest atomic heleprs even enforce this, to standardized the uabi more.
Imo everything else (in this case: make the flip complete on the same frame as the vblank, if you hit the vblank window) needs special flags, with clear meaning of what they do. The specific flip target sounds like a good idea, except that current userspace can't be fixed, so we need to make it work without any flag. And the new flag would be for flip-asap, or flip-variable-refresh or something like that. -Daniel
On 14.06.2016 17:06, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 04:25:28PM +0900, Michel Dänzer wrote:
On 14.06.2016 14:53, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote:
On 06/13/16 17:06, Daniel Vetter wrote: > > Afaiui the rules are: > - The timestamp for vblank event needs to agree with whatever oml_sync > requries. > - The event delivery itself needs to be consistent with what page_flip > takes, i.e. if userspace sees an event and immediately issues a > page_flip then it should not be able to hit the same vblank with that > pageflip. > [...]
> I assume you're goal is to not delay page_flips unecessarily, without > breaking requirement 2 here. Imo a simpler fix would be to delay the > vblank handling to end of vblank. Fixes everything without hacks, [...]
Except it breaks the original purpose of the wait for vblank functionality, which is to wait for the beginning of a vertical blank period. [0] You're focusing too much on page flips and suggesting to throw out the vblank baby with the bathwater. I really don't see the big issue which would justify that.
[0] As an analogy, how useful would e.g. calendar notifications be if they arrived at the end of the events they're about? "Hey, that meeting you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati?
Yes. With DRI3/Present, it's driver independent code in xserver/present/. With DRI2, it's theoretically up to the DDX driver, but all drivers seem to have basically the same logic; the modesetting driver certainly does.
Hm, didn't know that everyone does that. Seemed to silly an idea to waste all that gpu bandwidth by waiting for vblank ...
Actually it's kind of the other way around: One of the reasons for using sync-to-vblank is to save power for rendering stuff which cannot be seen anyway.
Also note that only the specific client using DRI2 or Present for presentation is blocked, nothing else.
I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever.
Please don't try to single out our drivers, it seems like rather your driver is the odd man out in this case.
Hm, why/where is i915 special?
By only triggering the vblank interrupt at the end of a vertical blank period, breaking the original DRM_IOCTL_WAIT_VBLANK functionality.
How bad would it really be to just always delay the page_flip past vblank?
In the variable refresh rate case it could be pretty bad, basically dropping to the minimum refresh rate.
Variable refresh rate is entirely undefined right now in kms.
I don't think that really matters for the issue I'm thinking of.
My understanding is that variable refresh rate basically works by transmitting the frame contents using the maximum refresh rate timing, and then dynamically extending the vertical blank period until either the next flip arrives, or the time since the last frame was transmitted corresponds to the minimum refresh rate. So if we always wait for the end of vertical blank before programming a flip, we'll probably end up degrading to the minimum refresh rate whenever we're already in vertical blank by the time we're ready to program the flip. Which will happen with any app which cannot sustain a framerate > the maximum refresh rate. So we'll end up running at either the minimum or maximum refresh rate (or possibly even worse, flip-flopping between the two), defeating the purpose of variable refresh rate.
Also, as I explained before, even without variable refresh rate, always delaying flip programming past vblank can cause flips to be unnecessarily delayed by one frame.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag).
That would be an inferior solution compared to my series, e.g.: If userspace calls DRM_IOCTL_MODE_PAGE_FLIP before the target vblank seqno is reached, it cannot use the new flag, otherwise the flip might take effect too early. However, if we are then already in the target vblank period when the fences have signalled and we are ready to program the flip, we have to wait for the end of vblank first, and the flip will be delayed by one frame.
If we're going to change the userspace interface, it would be better to re-purpose the reserved field of struct drm_mode_crtc_page_flip for explicitly specifying the target vblank seqno (via a new cap and flag). Then the kernel and userspace would no longer need to second-guess each other.
But even if we take that route, this series would be desirable for getting us most of the way there for existing userspace.
Well that's what I mean. You'r patches here shoehorn what you want into existing api, trying to second-guess userspaces intentions inferred from what it does. Ime that tends to end in trouble. It would be much better to have a clear uabi for this. And my flag was just a suggestion.
I just had a discussion on irc with Dave about another topic were Dave complained about some of the inferred abi rules SNA uses (entirely differently, in probe code). And I thought it was a nice idea, since hey it works and its easier. But really it's not, since in the end kms is supposed to be somewhat generic. And usually your nice idea for inferring behaviour then tends to break down somewhere. At least I think the generic kms rules are:
- vblank events fire at lockstep [...].
- pageflip immediately after a vblank wait needs to hit the next vblank.
- pageflip in a loop needs to result in at most 1 flip per vblank, and if you're too fast then the kernel should return -EBUSY. [...]
My series doesn't break any of these rules (or any others I'm aware of). It avoids unnecessarily delaying flips in some cases within the confines of these rules.
Imo everything else (in this case: make the flip complete on the same frame as the vblank, if you hit the vblank window) needs special flags, with clear meaning of what they do. The specific flip target sounds like a good idea, except that current userspace can't be fixed, so we need to make it work without any flag.
Hey, that was my point above! So you agree that (something like) this series will be needed anyway, even if new flags are added to make it more explicit? :)
On Wed, Jun 15, 2016 at 05:03:41PM +0900, Michel Dänzer wrote:
On 14.06.2016 17:06, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 04:25:28PM +0900, Michel Dänzer wrote:
On 14.06.2016 14:53, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
On 06/13/16 23:06, Daniel Vetter wrote:
On Mon, Jun 13, 2016 at 05:58:29PM +0900, Michel Dänzer wrote: > On 06/13/16 17:06, Daniel Vetter wrote: >> >> Afaiui the rules are: >> - The timestamp for vblank event needs to agree with whatever oml_sync >> requries. >> - The event delivery itself needs to be consistent with what page_flip >> takes, i.e. if userspace sees an event and immediately issues a >> page_flip then it should not be able to hit the same vblank with that >> pageflip. >> [...] > >> I assume you're goal is to not delay page_flips unecessarily, without >> breaking requirement 2 here. Imo a simpler fix would be to delay the >> vblank handling to end of vblank. Fixes everything without hacks, [...] > > Except it breaks the original purpose of the wait for vblank > functionality, which is to wait for the beginning of a vertical blank > period. [0] You're focusing too much on page flips and suggesting to > throw out the vblank baby with the bathwater. I really don't see the big > issue which would justify that. > > > [0] As an analogy, how useful would e.g. calendar notifications be if > they arrived at the end of the events they're about? "Hey, that meeting > you were supposed to attend? It just finished!"
Ok, what exactly is the use-case for waiting for vblanks _without_ scheduling a flip afterwards? At least in drm the rule is that ABI is what userspace observes and actually cares about.
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati?
Yes. With DRI3/Present, it's driver independent code in xserver/present/. With DRI2, it's theoretically up to the DDX driver, but all drivers seem to have basically the same logic; the modesetting driver certainly does.
Hm, didn't know that everyone does that. Seemed to silly an idea to waste all that gpu bandwidth by waiting for vblank ...
Actually it's kind of the other way around: One of the reasons for using sync-to-vblank is to save power for rendering stuff which cannot be seen anyway.
Also note that only the specific client using DRI2 or Present for presentation is blocked, nothing else.
I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever.
Please don't try to single out our drivers, it seems like rather your driver is the odd man out in this case.
Hm, why/where is i915 special?
By only triggering the vblank interrupt at the end of a vertical blank period, breaking the original DRM_IOCTL_WAIT_VBLANK functionality.
Ok, turns out we never did that, but we did move the drm event for page flip completion around. So indeed vblank wait drm event should fire at start of vblank if possible. I still maintain that (by default) you shouldn't allow a page flip to overtake a drm event.
How bad would it really be to just always delay the page_flip past vblank?
In the variable refresh rate case it could be pretty bad, basically dropping to the minimum refresh rate.
Variable refresh rate is entirely undefined right now in kms.
I don't think that really matters for the issue I'm thinking of.
My understanding is that variable refresh rate basically works by transmitting the frame contents using the maximum refresh rate timing, and then dynamically extending the vertical blank period until either the next flip arrives, or the time since the last frame was transmitted corresponds to the minimum refresh rate. So if we always wait for the end of vertical blank before programming a flip, we'll probably end up degrading to the minimum refresh rate whenever we're already in vertical blank by the time we're ready to program the flip. Which will happen with any app which cannot sustain a framerate > the maximum refresh rate. So we'll end up running at either the minimum or maximum refresh rate (or possibly even worse, flip-flopping between the two), defeating the purpose of variable refresh rate.
Also, as I explained before, even without variable refresh rate, always delaying flip programming past vblank can cause flips to be unnecessarily delayed by one frame.
Yes, but right now you show them too early, breaking existing stuff. My stance is that you need an explicit flag to tell the kernel which one you want (userspace tells you already by either asking for a specific frame, or for "as soon as possible"). I don't like second-guessing userspace. And yes that means that for variable vrefresh you probably need to run it at 60Hz by default, except when userspace set a special mode flag which allows variable vrefresh, telling the kernel that it knows things can get slow if it doesn't ask for asap.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag).
That would be an inferior solution compared to my series, e.g.: If userspace calls DRM_IOCTL_MODE_PAGE_FLIP before the target vblank seqno is reached, it cannot use the new flag, otherwise the flip might take effect too early. However, if we are then already in the target vblank period when the fences have signalled and we are ready to program the flip, we have to wait for the end of vblank first, and the flip will be delayed by one frame.
If we're going to change the userspace interface, it would be better to re-purpose the reserved field of struct drm_mode_crtc_page_flip for explicitly specifying the target vblank seqno (via a new cap and flag). Then the kernel and userspace would no longer need to second-guess each other.
But even if we take that route, this series would be desirable for getting us most of the way there for existing userspace.
Well that's what I mean. You'r patches here shoehorn what you want into existing api, trying to second-guess userspaces intentions inferred from what it does. Ime that tends to end in trouble. It would be much better to have a clear uabi for this. And my flag was just a suggestion.
I just had a discussion on irc with Dave about another topic were Dave complained about some of the inferred abi rules SNA uses (entirely differently, in probe code). And I thought it was a nice idea, since hey it works and its easier. But really it's not, since in the end kms is supposed to be somewhat generic. And usually your nice idea for inferring behaviour then tends to break down somewhere. At least I think the generic kms rules are:
- vblank events fire at lockstep [...].
- pageflip immediately after a vblank wait needs to hit the next vblank.
- pageflip in a loop needs to result in at most 1 flip per vblank, and if you're too fast then the kernel should return -EBUSY. [...]
My series doesn't break any of these rules (or any others I'm aware of). It avoids unnecessarily delaying flips in some cases within the confines of these rules.
Imo everything else (in this case: make the flip complete on the same frame as the vblank, if you hit the vblank window) needs special flags, with clear meaning of what they do. The specific flip target sounds like a good idea, except that current userspace can't be fixed, so we need to make it work without any flag.
Hey, that was my point above! So you agree that (something like) this series will be needed anyway, even if new flags are added to make it more explicit? :)
Yeah I think there's a bit of confusion going on here ;-) Of course I'm not against fixing this, and I agree that fixing it by delaying the vblank drm event (like I proposed at first) is not good. What I think would be best to fix this:
- For all current userspace (i.e. no flags or anything) force vrefresh to to be fixed, and delay page flips which hit the vblank window to be after that. This way amd drivers are consistent with every other kms drivers, and work like current userspace seems to expect: Wait for vblank, then assume any flips will only hit after the next vblank.
- For clients which don't care about which frame to be displayed on, add a flag to page_flip (and atomic_commit) that asks for asap, but still without tearing. With atomic we even want to be able to overwrite older flips, to reduce latency as much as possible for clients who can render more frames than vrefresh.
- For variable vrefresh I think we need yet another flag (crtc property, or mode flag) so that userspace can tell the kernel when it's ok to have vblank times with massive jitter. Again default should be current mode. Userspace can then enable variable vrefresh when it only has clients which don't care when exactly they show up. As soon as something shows up which asks for precise timestamps and displaying of the flip (using OML_sync_control or Present), userspace can disable the variable vrefresh mode again to get back to a lockstep 60Hz (or whatever it is).
- Anyone using WAIT_VBLANK behind the compositors back might be in even more trouble, but imo we shouldn't give too much concern to that case. Instead apply more pressure for everyone to switch over to Present or OML_sync_control (and we need that for EGL, too).
That way there's no second-guessing of userspace intentions by watching vblank waits, it should be possible to extend for variable refresh and benchmark/low-latency mode, and we don't need special driver hacks in core code either. Thoughts on whether this plan would fit you too?
Cheers, Daniel
On 15.06.2016 18:23, Daniel Vetter wrote:
On Wed, Jun 15, 2016 at 05:03:41PM +0900, Michel Dänzer wrote:
On 14.06.2016 17:06, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 04:25:28PM +0900, Michel Dänzer wrote:
On 14.06.2016 14:53, Daniel Vetter wrote:
I didn't know that we pass vblank waits to X clients. Either way annoying, since it means you need to keep things working like this for amd drivers forever.
Please don't try to single out our drivers, it seems like rather your driver is the odd man out in this case.
Hm, why/where is i915 special?
By only triggering the vblank interrupt at the end of a vertical blank period, breaking the original DRM_IOCTL_WAIT_VBLANK functionality.
Ok, turns out we never did that, but we did move the drm event for page flip completion around. So indeed vblank wait drm event should fire at start of vblank if possible. I still maintain that (by default) you shouldn't allow a page flip to overtake a drm event.
We don't allow that AFAIK. If you think we do, please describe the scenario you're thinking of.
The only thing I can think of is that you may be concerned about cases where userspace calls DRM_IOCTL_MODE_PAGE_FLIP several times in a row without calling DRM_IOCTL_WAIT_VBLANK in between. If so, I can change patch 2 to also track page flip completions in file_priv->last_vblank_wait. That would ensure that two consecutive flips can never complete in the same vertical blank period.
How bad would it really be to just always delay the page_flip past vblank?
[...]
[...] always delaying flip programming past vblank can cause flips to be unnecessarily delayed by one frame.
Yes, but right now you show them too early, breaking existing stuff.
No, we don't! Neither before this series nor after it, nor at any point during it.
The DRI2 code in our DDX drivers actually checks for this and complains if a flip completes earlier than expected. We did break this before and received bug reports about it. Mario fixed it by changing the MASTER_UPDATE_MODE register to 3, which restricts flips to take effect only at the beginning of vertical blank. This series makes it safe to change it back to 0 (allowing flips to take effect anywhere in vertical blank) and then does so.
If that's not good enough I'd say we should add a faster-than-vblank-but-still-synced page_flip flag. Then userspace could tell you exactly whether you should always wait (no flags), or never wait (with this new flag).
That would be an inferior solution compared to my series, e.g.: If userspace calls DRM_IOCTL_MODE_PAGE_FLIP before the target vblank seqno is reached, it cannot use the new flag, otherwise the flip might take effect too early. However, if we are then already in the target vblank period when the fences have signalled and we are ready to program the flip, we have to wait for the end of vblank first, and the flip will be delayed by one frame.
If we're going to change the userspace interface, it would be better to re-purpose the reserved field of struct drm_mode_crtc_page_flip for explicitly specifying the target vblank seqno (via a new cap and flag). Then the kernel and userspace would no longer need to second-guess each other.
But even if we take that route, this series would be desirable for getting us most of the way there for existing userspace.
Well that's what I mean. You'r patches here shoehorn what you want into existing api, trying to second-guess userspaces intentions inferred from what it does. Ime that tends to end in trouble. It would be much better to have a clear uabi for this. And my flag was just a suggestion.
[...] At least I think the generic kms rules are:
- vblank events fire at lockstep [...].
- pageflip immediately after a vblank wait needs to hit the next vblank.
- pageflip in a loop needs to result in at most 1 flip per vblank, and if you're too fast then the kernel should return -EBUSY. [...]
My series doesn't break any of these rules (or any others I'm aware of). It avoids unnecessarily delaying flips in some cases within the confines of these rules.
Imo everything else (in this case: make the flip complete on the same frame as the vblank, if you hit the vblank window) needs special flags, with clear meaning of what they do. The specific flip target sounds like a good idea, except that current userspace can't be fixed, so we need to make it work without any flag.
Hey, that was my point above! So you agree that (something like) this series will be needed anyway, even if new flags are added to make it more explicit? :)
Yeah I think there's a bit of confusion going on here ;-) Of course I'm not against fixing this, and I agree that fixing it by delaying the vblank drm event (like I proposed at first) is not good. What I think would be best to fix this:
- For all current userspace (i.e. no flags or anything) force vrefresh to to be fixed, and delay page flips which hit the vblank window to be after that. This way amd drivers are consistent with every other kms drivers, and work like current userspace seems to expect: Wait for vblank, then assume any flips will only hit after the next vblank.
This series preserves this behaviour. A flip is only allowed to complete during the current vertical blank period if userspace either:
* expected it to complete in this vertical blank (or an earlier one). In other words, if the flip doesn't complete in this vertical blank, it is delayed (further) compared to userspace expectations.
* hasn't called DRM_IOCTL_WAIT_VBLANK at all (so apparently it doesn't care about when the flip completes).
It sounds like you're saying we aren't allowed to fix cases where flips are completing later than expected by userspace, because other drivers haven't fixed those cases yet. Quite frankly, that sucks. Nothing other than possible hardware restrictions prevents other drivers from fixing this as well.
- For clients which don't care about which frame to be displayed on, add a flag to page_flip (and atomic_commit) that asks for asap, but still without tearing.
I explained above why such a flag wouldn't help in all cases. When I get a chance, I'll work on a series allowing the target vblank seqno to be specified explicitly in DRM_IOCTL_MODE_PAGE_FLIP. That should cover all cases.
- For variable vrefresh I think we need yet another flag (crtc property, or mode flag) so that userspace can tell the kernel when it's ok to have vblank times with massive jitter. Again default should be current mode. Userspace can then enable variable vrefresh when it only has clients which don't care when exactly they show up. As soon as something shows up which asks for precise timestamps and displaying of the flip (using OML_sync_control or Present), userspace can disable the variable vrefresh mode again to get back to a lockstep 60Hz (or whatever it is).
Colour me skeptical about that being a good approach for variable refresh rate, but that's another discussion which doesn't directly affect this series.
On Thu, Jun 16, 2016 at 11:15:14AM +0900, Michel Dänzer wrote:
On 15.06.2016 18:23, Daniel Vetter wrote:
On Wed, Jun 15, 2016 at 05:03:41PM +0900, Michel Dänzer wrote:
On 14.06.2016 17:06, Daniel Vetter wrote:
Yeah I think there's a bit of confusion going on here ;-) Of course I'm not against fixing this, and I agree that fixing it by delaying the vblank drm event (like I proposed at first) is not good. What I think would be best to fix this:
- For all current userspace (i.e. no flags or anything) force vrefresh to to be fixed, and delay page flips which hit the vblank window to be after that. This way amd drivers are consistent with every other kms drivers, and work like current userspace seems to expect: Wait for vblank, then assume any flips will only hit after the next vblank.
This series preserves this behaviour. A flip is only allowed to complete during the current vertical blank period if userspace either:
expected it to complete in this vertical blank (or an earlier one). In other words, if the flip doesn't complete in this vertical blank, it is delayed (further) compared to userspace expectations.
hasn't called DRM_IOCTL_WAIT_VBLANK at all (so apparently it doesn't care about when the flip completes).
It sounds like you're saying we aren't allowed to fix cases where flips are completing later than expected by userspace, because other drivers haven't fixed those cases yet. Quite frankly, that sucks. Nothing other than possible hardware restrictions prevents other drivers from fixing this as well.
I'm not objecting against fixing this. I'm objecting against fixing this through clever inferring of what userspace wants, aka the above, instead of an explicit flag or something. And without that flag the rule is that a pageflip after vblank hits the next vblank and can't squeeze into the current one. -Daniel
On Tue, Jun 14, 2016 at 07:53:41AM +0200, Daniel Vetter wrote:
On Tue, Jun 14, 2016 at 11:09:10AM +0900, Michel Dänzer wrote:
E.g.: In cases where page flipping cannot be used, Xorg / the DDX driver waits for the target vertical blank period before emitting the drawing commands for a buffer swap operation. If the vblank notification only arrives when the vertical blank period is already over, this is very likely to result in tearing.
Some X compositors and AFAIK even applications such as media players can use DRM_IOCTL_WAIT_VBLANK similarly. Obviously it's not intended to be used directly like that, but nonetheless it is.
Is there really anything using it like that outside of -ati? I didn't know that we pass vblank waits to X clients.
No, because EGL doesn't offer an equivalent to OML_sync_control applications like kodi have implemented their own vblank scheduling via DRM_IOCTL_WAIT_VBLANK directly.
Either way annoying, since it means you need to keep things working like this for amd drivers forever. Afaik others don't use it like that, at least not on intel. Weston has some hacks to use vblank waits for plane flips, but that's all disabled code because it just doesn't work - you need full atomic.
Inside Xorg/Present, as Michel said, the vblank notification is used to drive onscreen copies *within* the vblank period (i.e. to try and avoid visible tearing). -Chris
From: Michel Dänzer michel.daenzer@amd.com
With the previous change, it's safe to let page flips take effect anytime during a vertical blank period.
This can avoid delaying a flip by a frame in some cases where we only get to amdgpu_flip_work_func -> adev->mode_info.funcs->page_flip during the target vertical blank period.
Signed-off-by: Michel Dänzer michel.daenzer@amd.com --- drivers/gpu/drm/amd/amdgpu/dce_v10_0.c | 8 ++++---- drivers/gpu/drm/amd/amdgpu/dce_v11_0.c | 4 ++-- drivers/gpu/drm/amd/amdgpu/dce_v8_0.c | 8 ++++---- 3 files changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c index be1cf38..99a4638 100644 --- a/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c +++ b/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c @@ -646,8 +646,8 @@ static void dce_v10_0_resume_mc_access(struct amdgpu_device *adev,
if (save->crtc_enabled[i]) { tmp = RREG32(mmMASTER_UPDATE_MODE + crtc_offsets[i]); - if (REG_GET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE) != 3) { - tmp = REG_SET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE, 3); + if (REG_GET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE) != 0) { + tmp = REG_SET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE, 0); WREG32(mmMASTER_UPDATE_MODE + crtc_offsets[i], tmp); } tmp = RREG32(mmGRPH_UPDATE + crtc_offsets[i]); @@ -2275,8 +2275,8 @@ static int dce_v10_0_crtc_do_set_base(struct drm_crtc *crtc, WREG32(mmVIEWPORT_SIZE + amdgpu_crtc->crtc_offset, (viewport_w << 16) | viewport_h);
- /* set pageflip to happen only at start of vblank interval (front porch) */ - WREG32(mmMASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 3); + /* set pageflip to happen anywhere in vblank interval */ + WREG32(mmMASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 0);
if (!atomic && fb && fb != crtc->primary->fb) { amdgpu_fb = to_amdgpu_framebuffer(fb); diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c index cd2ec81..44f0d22 100644 --- a/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c +++ b/drivers/gpu/drm/amd/amdgpu/dce_v11_0.c @@ -2251,8 +2251,8 @@ static int dce_v11_0_crtc_do_set_base(struct drm_crtc *crtc, WREG32(mmVIEWPORT_SIZE + amdgpu_crtc->crtc_offset, (viewport_w << 16) | viewport_h);
- /* set pageflip to happen only at start of vblank interval (front porch) */ - WREG32(mmCRTC_MASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 3); + /* set pageflip to happen anywhere in vblank interval */ + WREG32(mmCRTC_MASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 0);
if (!atomic && fb && fb != crtc->primary->fb) { amdgpu_fb = to_amdgpu_framebuffer(fb); diff --git a/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c b/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c index c087f93..86864dd 100644 --- a/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c +++ b/drivers/gpu/drm/amd/amdgpu/dce_v8_0.c @@ -591,8 +591,8 @@ static void dce_v8_0_resume_mc_access(struct amdgpu_device *adev,
if (save->crtc_enabled[i]) { tmp = RREG32(mmMASTER_UPDATE_MODE + crtc_offsets[i]); - if (REG_GET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE) != 3) { - tmp = REG_SET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE, 3); + if (REG_GET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE) != 0) { + tmp = REG_SET_FIELD(tmp, MASTER_UPDATE_MODE, MASTER_UPDATE_MODE, 0); WREG32(mmMASTER_UPDATE_MODE + crtc_offsets[i], tmp); } tmp = RREG32(mmGRPH_UPDATE + crtc_offsets[i]); @@ -2190,8 +2190,8 @@ static int dce_v8_0_crtc_do_set_base(struct drm_crtc *crtc, WREG32(mmVIEWPORT_SIZE + amdgpu_crtc->crtc_offset, (viewport_w << 16) | viewport_h);
- /* set pageflip to happen only at start of vblank interval (front porch) */ - WREG32(mmMASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 3); + /* set pageflip to happen anywhere in vblank interval */ + WREG32(mmMASTER_UPDATE_MODE + amdgpu_crtc->crtc_offset, 0);
if (!atomic && fb && fb != crtc->primary->fb) { amdgpu_fb = to_amdgpu_framebuffer(fb);
Am 10.06.2016 um 10:57 schrieb Michel Dänzer:
The main purpose of this series is patch 5, which can avoid delaying flips for a frame in some cases. It depends on patch 4 to prevent flips from taking effect too early, which in turn depends on the core DRM patch 2.
Patches 1 & 3 are cleanups I noticed while working on the other patches.
Mario, it would be great if you could run these through your rigorous vblank testing.
[PATCH 1/5] drm: Only handle _DRM_VBLANK_NEXTONMISS once [PATCH 2/5] drm: Keep track of last vblank sequence waited for
Acked-by: Christian König christian.koenig@amd.com for those two.
[PATCH 3/5] drm/amdgpu: Unpin BO if we can't get fences in [PATCH 4/5] drm/amdgpu: Wait for end of last waited-for vblank before [PATCH 5/5] drm/amdgpu: Set MASTER_UPDATE_MODE to 0 again
Reviewed-by: Christian König christian.koenig@amd.com for those three.
Cheers, Christian.
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Chris Wilson -
Christian König -
Daniel Vetter -
Michel Dänzer