Re: [PATCH 2/4] drm/vmwgfx: Defer fence irq processing to a tasklet

On Fri, Oct 30, 2015 at 02:42:44AM -0700, Thomas Hellstrom wrote:

Reduce the time in hardware irq context and hardware irq latency.

Signed-off-by: Thomas Hellstrom thellstrom@vmware.com Reviewed-by: Sinclair Yeh syeh@vmware.com

---

drivers/gpu/drm/vmwgfx/vmwgfx_fence.c | 108 ++++++++++++++++++++-------------- drivers/gpu/drm/vmwgfx/vmwgfx_fence.h | 2 + drivers/gpu/drm/vmwgfx/vmwgfx_irq.c | 6 +- 3 files changed, 68 insertions(+), 48 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c index 8e689b4..f40c36e 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.c @@ -47,6 +47,7 @@ struct vmw_fence_manager { bool seqno_valid; /* Protected by @lock, and may not be set to true without the @goal_irq_mutex held. */ unsigned ctx;

• struct tasklet_struct tasklet;

Bottom halves are super-deprecated except for giant existing users like networking. I think the recommended way to do this is to either use threaded interrupts or work-queues. The reason for that seems to be that locking is funky around them, which is a major pain for RT. And RT is going mainline now for real. -Daniel

};

struct vmw_user_fence { @@ -81,6 +82,8 @@ struct vmw_event_fence_action { uint32_t *tv_usec; };

+static void vmw_fence_tasklet(unsigned long data);

static struct vmw_fence_manager * fman_from_fence(struct vmw_fence_obj *fence) { @@ -115,12 +118,11 @@ static void vmw_fence_obj_destroy(struct fence *f) container_of(f, struct vmw_fence_obj, base);

struct vmw_fence_manager *fman = fman_from_fence(fence);

• unsigned long irq_flags;

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); list_del_init(&fence->head); --fman->num_fence_objects;

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock); fence->destroy(fence);

}

@@ -177,7 +179,6 @@ static long vmw_fence_wait(struct fence *f, bool intr, signed long timeout) struct vmw_private *dev_priv = fman->dev_priv; struct vmwgfx_wait_cb cb; long ret = timeout;

• unsigned long irq_flags;

  if (likely(vmw_fence_obj_signaled(fence))) return timeout;

@@ -185,7 +186,7 @@ static long vmw_fence_wait(struct fence *f, bool intr, signed long timeout) vmw_fifo_ping_host(dev_priv, SVGA_SYNC_GENERIC); vmw_seqno_waiter_add(dev_priv);

• spin_lock_irqsave(f->lock, irq_flags);

• spin_lock_bh(f->lock);

  if (intr && signal_pending(current)) { ret = -ERESTARTSYS;

@@ -205,11 +206,11 @@ static long vmw_fence_wait(struct fence *f, bool intr, signed long timeout) __set_current_state(TASK_INTERRUPTIBLE); else __set_current_state(TASK_UNINTERRUPTIBLE);

• spin_unlock_irqrestore(f->lock, irq_flags);
  

• spin_unlock_bh(f->lock);
  
  

  ret = schedule_timeout(ret);

• spin_lock_irqsave(f->lock, irq_flags);
  

• spin_lock_bh(f->lock);
  

  if (ret > 0 && intr && signal_pending(current)) ret = -ERESTARTSYS; }

@@ -219,7 +220,7 @@ static long vmw_fence_wait(struct fence *f, bool intr, signed long timeout) __set_current_state(TASK_RUNNING);

out:

• spin_unlock_irqrestore(f->lock, irq_flags);

• spin_unlock_bh(f->lock);

  vmw_seqno_waiter_remove(dev_priv);

@@ -300,21 +301,22 @@ struct vmw_fence_manager *vmw_fence_manager_init(struct vmw_private *dev_priv) ttm_round_pot(sizeof(struct vmw_event_fence_action)); mutex_init(&fman->goal_irq_mutex); fman->ctx = fence_context_alloc(1);

• tasklet_init(&fman->tasklet, vmw_fence_tasklet,

•      (unsigned long) fman);
  
  

  return fman;

}

void vmw_fence_manager_takedown(struct vmw_fence_manager *fman) {

• unsigned long irq_flags; bool lists_empty;

  (void) cancel_work_sync(&fman->work);

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); lists_empty = list_empty(&fman->fence_list) && list_empty(&fman->cleanup_list);

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

  BUG_ON(!lists_empty); kfree(fman);

@@ -324,7 +326,6 @@ static int vmw_fence_obj_init(struct vmw_fence_manager *fman, struct vmw_fence_obj *fence, u32 seqno, void (*destroy) (struct vmw_fence_obj *fence)) {

• unsigned long irq_flags; int ret = 0;

  fence_init(&fence->base, &vmw_fence_ops, &fman->lock,

@@ -332,7 +333,7 @@ static int vmw_fence_obj_init(struct vmw_fence_manager *fman, INIT_LIST_HEAD(&fence->seq_passed_actions); fence->destroy = destroy;

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); if (unlikely(fman->fifo_down)) { ret = -EBUSY; goto out_unlock;

@@ -341,7 +342,7 @@ static int vmw_fence_obj_init(struct vmw_fence_manager *fman, ++fman->num_fence_objects;

out_unlock:

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock); return ret;

} @@ -490,11 +491,9 @@ rerun:

void vmw_fences_update(struct vmw_fence_manager *fman) {

• unsigned long irq_flags;
• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); __vmw_fences_update(fman);

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

}

bool vmw_fence_obj_signaled(struct vmw_fence_obj *fence) @@ -694,11 +693,9 @@ void vmw_fence_fifo_down(struct vmw_fence_manager *fman)

void vmw_fence_fifo_up(struct vmw_fence_manager *fman) {

• unsigned long irq_flags;
• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); fman->fifo_down = false;

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

}

@@ -825,10 +822,9 @@ void vmw_event_fence_fpriv_gone(struct vmw_fence_manager *fman, { struct vmw_event_fence_action *eaction; struct drm_pending_event *event;

• unsigned long irq_flags;

  while (1) {

• spin_lock_irqsave(&fman->lock, irq_flags);
  

• spin_lock_bh(&fman->lock);
  

  if (list_empty(event_list)) goto out_unlock; eaction = list_first_entry(event_list,

@@ -837,11 +833,11 @@ void vmw_event_fence_fpriv_gone(struct vmw_fence_manager *fman, list_del_init(&eaction->fpriv_head); event = eaction->event; eaction->event = NULL;

• spin_unlock_irqrestore(&fman->lock, irq_flags);
  

• spin_unlock_bh(&fman->lock);
  

  event->destroy(event); }

out_unlock:

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

}

@@ -854,7 +850,7 @@ out_unlock:

• This function is called when the seqno of the fence where @action is
• attached has passed. It queues the event on the submitter's event list.
• This function is always called from atomic context, and may be called

• • from irq context.

• • from tasklet context.
  */

static void vmw_event_fence_action_seq_passed(struct vmw_fence_action *action) { @@ -863,13 +859,12 @@ static void vmw_event_fence_action_seq_passed(struct vmw_fence_action *action) struct drm_device *dev = eaction->dev; struct drm_pending_event *event = eaction->event; struct drm_file *file_priv;

• unsigned long irq_flags;

  if (unlikely(event == NULL)) return;

  file_priv = event->file_priv;

• spin_lock_irqsave(&dev->event_lock, irq_flags);

• spin_lock_bh(&dev->event_lock);

  if (likely(eaction->tv_sec != NULL)) { struct timeval tv;

@@ -883,7 +878,7 @@ static void vmw_event_fence_action_seq_passed(struct vmw_fence_action *action) list_add_tail(&eaction->event->link, &file_priv->event_list); eaction->event = NULL; wake_up_all(&file_priv->event_wait);

• spin_unlock_irqrestore(&dev->event_lock, irq_flags);

• spin_unlock_bh(&dev->event_lock);

}

/** @@ -900,11 +895,10 @@ static void vmw_event_fence_action_cleanup(struct vmw_fence_action *action) struct vmw_event_fence_action *eaction = container_of(action, struct vmw_event_fence_action, action); struct vmw_fence_manager *fman = fman_from_fence(eaction->fence);

• unsigned long irq_flags;

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); list_del(&eaction->fpriv_head);

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

  vmw_fence_obj_unreference(&eaction->fence); kfree(eaction);

@@ -924,11 +918,10 @@ static void vmw_fence_obj_add_action(struct vmw_fence_obj *fence, struct vmw_fence_action *action) { struct vmw_fence_manager *fman = fman_from_fence(fence);

• unsigned long irq_flags; bool run_update = false;

  mutex_lock(&fman->goal_irq_mutex);

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock);

  fman->pending_actions[action->type]++; if (fence_is_signaled_locked(&fence->base)) {

@@ -947,7 +940,7 @@ static void vmw_fence_obj_add_action(struct vmw_fence_obj *fence, run_update = vmw_fence_goal_check_locked(fence); }

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

  if (run_update) { if (!fman->goal_irq_on) {

@@ -985,7 +978,6 @@ int vmw_event_fence_action_queue(struct drm_file *file_priv, struct vmw_event_fence_action *eaction; struct vmw_fence_manager *fman = fman_from_fence(fence); struct vmw_fpriv *vmw_fp = vmw_fpriv(file_priv);

• unsigned long irq_flags;

  eaction = kzalloc(sizeof(*eaction), GFP_KERNEL); if (unlikely(eaction == NULL))

@@ -1002,9 +994,9 @@ int vmw_event_fence_action_queue(struct drm_file *file_priv, eaction->tv_sec = tv_sec; eaction->tv_usec = tv_usec;

• spin_lock_irqsave(&fman->lock, irq_flags);

• spin_lock_bh(&fman->lock); list_add_tail(&eaction->fpriv_head, &vmw_fp->fence_events);

• spin_unlock_irqrestore(&fman->lock, irq_flags);

• spin_unlock_bh(&fman->lock);

  vmw_fence_obj_add_action(fence, &eaction->action);

@@ -1025,16 +1017,15 @@ static int vmw_event_fence_action_create(struct drm_file *file_priv, struct vmw_event_fence_pending *event; struct vmw_fence_manager *fman = fman_from_fence(fence); struct drm_device *dev = fman->dev_priv->dev;

• unsigned long irq_flags; int ret;

• spin_lock_irqsave(&dev->event_lock, irq_flags);

• spin_lock_bh(&dev->event_lock);

  ret = (file_priv->event_space < sizeof(event->event)) ? -EBUSY : 0; if (likely(ret == 0)) file_priv->event_space -= sizeof(event->event);

• spin_unlock_irqrestore(&dev->event_lock, irq_flags);

• spin_unlock_bh(&dev->event_lock);

  if (unlikely(ret != 0)) { DRM_ERROR("Failed to allocate event space for this file.\n");

@@ -1078,9 +1069,9 @@ static int vmw_event_fence_action_create(struct drm_file *file_priv, out_no_queue: event->base.destroy(&event->base); out_no_event:

• spin_lock_irqsave(&dev->event_lock, irq_flags);

• spin_lock_bh(&dev->event_lock); file_priv->event_space += sizeof(*event);

• spin_unlock_irqrestore(&dev->event_lock, irq_flags);

• spin_unlock_bh(&dev->event_lock);

out_no_space: return ret; } @@ -1172,3 +1163,32 @@ out_no_ref_obj: vmw_fence_obj_unreference(&fence); return ret; }

+/**

• • vmw_fence_tasklet - Fence manager tasklet entry point
• • @data: The tasklet closure - A pointer to the fence manager cast to an
• • unsigned long.
• */

+static void vmw_fence_tasklet(unsigned long data) +{

• struct vmw_fence_manager *fman = (struct vmw_fence_manager *) data;
• spin_lock(&fman->lock);
• __vmw_fences_update(fman);
• spin_unlock(&fman->lock);
• wake_up_all(&fman->dev_priv->fence_queue);

+}

+/**

• • vmw_fence_tasklet_schedule - Schedule a fence manager tasklet run
• • @fman: Pointer to a fence manager
• */

+void vmw_fence_tasklet_schedule(struct vmw_fence_manager *fman) +{

• if (!fman)

• return;
  

• tasklet_schedule(&fman->tasklet);

+} diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h index 8be6c29..e55b2c9 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fence.h @@ -124,4 +124,6 @@ extern int vmw_event_fence_action_queue(struct drm_file *filee_priv, uint32_t *tv_sec, uint32_t *tv_usec, bool interruptible); +extern void vmw_fence_tasklet_schedule(struct vmw_fence_manager *fman);

#endif /* _VMWGFX_FENCE_H_ */ diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c b/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c index ac3eccd..b0a6e65 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_irq.c @@ -48,10 +48,8 @@ irqreturn_t vmw_irq_handler(int irq, void *arg) return IRQ_NONE;

if (masked_status & (SVGA_IRQFLAG_ANY_FENCE |

• 	     SVGA_IRQFLAG_FENCE_GOAL)) {
  

• vmw_fences_update(dev_priv->fman);
  

• wake_up_all(&dev_priv->fence_queue);
  

• }

• 	     SVGA_IRQFLAG_FENCE_GOAL))
  

• vmw_fence_tasklet_schedule(dev_priv->fman);
  
  

  if (masked_status & SVGA_IRQFLAG_FIFO_PROGRESS) wake_up_all(&dev_priv->fifo_queue);

-- 2.4.3

---

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