Am 08.07.21 um 13:20 schrieb Daniel Vetter:
On Thu, Jul 8, 2021 at 12:54 PM Christian König christian.koenig@amd.com wrote:
[SNIP]
As far as I know that not completely correct. The rules around atomics i once learned are:
- Everything which modifies something is a write barrier.
- Everything which returns something is a read barrier.
And I know a whole bunch of use cases where this is relied upon in the core kernel, so I'm pretty sure that's correct.
That's against what the doc says, and also it would mean stuff like atomic_read_acquire or smp_mb__after/before_atomic is completely pointless.
On x86 you're right, anywhere else where there's no total store ordering I you're wrong.
Good to know. I always thought that atomic_read_acquire() was just for documentation purpose.
Maybe you mixed it up with C++ atomics (which I think are now also in C)? Those are strongly ordered by default (you can get the weakly ordered kernel-style one too). It's a bit unfortunate that the default semantics are exactly opposite between kernel and userspace :-/
Yeah, that's most likely it.
If there's code that relies on this it needs to be fixed and properly documented. I did go through the squeue code a bit, and might be better to just replace this with a core data structure.
Well the spsc was especially crafted for this use case and performed quite a bit better then a double linked list.
Yeah double-linked list is awful.
Or what core data structure do you have in mind?
Hm I thought there's a ready-made queue primitive, but there's just llist.h. Which I think is roughly what the scheduler queue also does. Minus the atomic_t for counting how many there are, and aside from the tracepoints I don't think we're using those anywhere, we just check for is_empty in the code (from a quick look only).
I think we just need to replace the atomic_read() with atomic_read_acquire() and the atomic_dec() with atomic_dec_return_release().
Apart from that everything should be working as far as I can see. And yes llist.h doesn't really do much different, it just doesn't keeps a tail pointer.
Christian.
-Daniel
Christian.
-Daniel
In this case the write barrier is the atomic_dec() in spsc_queue_pop() and the read barrier is the aromic_read() in spsc_queue_count().
The READ_ONCE() is actually not even necessary as far as I can see.
Christian.
-Daniel
atomic op, then it's a full barrier. So yeah you need more here. But also since you only need a read barrier on one side, and a write barrier on the other, you don't actually need a cpu barriers on x86. And READ_ONCE gives you the compiler barrier on one side at least, I haven't found it on the writer side yet.
> But yes a comment would be really nice here. I had to think for a while > why we don't need this as well. I'm typing a patch, which after a night's sleep I realized has the wrong barriers. And now I'm also typing some doc improvements for drm_sched_entity and related functions.
> Christian. > >> -Daniel >> >>> Christian. >>> >>> >>>> -Daniel >>>> >>>>> Regards >>>>> Christian. >>>>> >>>>>> -Daniel >>>>>> >>>>>>> Christian. >>>>>>> >>>>>>>> Also improve the kerneldoc for this. >>>>>>>> >>>>>>>> Acked-by: Steven Price steven.price@arm.com (v2) >>>>>>>> Signed-off-by: Daniel Vetter daniel.vetter@intel.com >>>>>>>> Cc: Lucas Stach l.stach@pengutronix.de >>>>>>>> Cc: Russell King linux+etnaviv@armlinux.org.uk >>>>>>>> Cc: Christian Gmeiner christian.gmeiner@gmail.com >>>>>>>> Cc: Qiang Yu yuq825@gmail.com >>>>>>>> Cc: Rob Herring robh@kernel.org >>>>>>>> Cc: Tomeu Vizoso tomeu.vizoso@collabora.com >>>>>>>> Cc: Steven Price steven.price@arm.com >>>>>>>> Cc: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com >>>>>>>> Cc: David Airlie airlied@linux.ie >>>>>>>> Cc: Daniel Vetter daniel@ffwll.ch >>>>>>>> Cc: Sumit Semwal sumit.semwal@linaro.org >>>>>>>> Cc: "Christian König" christian.koenig@amd.com >>>>>>>> Cc: Masahiro Yamada masahiroy@kernel.org >>>>>>>> Cc: Kees Cook keescook@chromium.org >>>>>>>> Cc: Adam Borowski kilobyte@angband.pl >>>>>>>> Cc: Nick Terrell terrelln@fb.com >>>>>>>> Cc: Mauro Carvalho Chehab mchehab+huawei@kernel.org >>>>>>>> Cc: Paul Menzel pmenzel@molgen.mpg.de >>>>>>>> Cc: Sami Tolvanen samitolvanen@google.com >>>>>>>> Cc: Viresh Kumar viresh.kumar@linaro.org >>>>>>>> Cc: Alex Deucher alexander.deucher@amd.com >>>>>>>> Cc: Dave Airlie airlied@redhat.com >>>>>>>> Cc: Nirmoy Das nirmoy.das@amd.com >>>>>>>> Cc: Deepak R Varma mh12gx2825@gmail.com >>>>>>>> Cc: Lee Jones lee.jones@linaro.org >>>>>>>> Cc: Kevin Wang kevin1.wang@amd.com >>>>>>>> Cc: Chen Li chenli@uniontech.com >>>>>>>> Cc: Luben Tuikov luben.tuikov@amd.com >>>>>>>> Cc: "Marek Olšák" marek.olsak@amd.com >>>>>>>> Cc: Dennis Li Dennis.Li@amd.com >>>>>>>> Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com >>>>>>>> Cc: Andrey Grodzovsky andrey.grodzovsky@amd.com >>>>>>>> Cc: Sonny Jiang sonny.jiang@amd.com >>>>>>>> Cc: Boris Brezillon boris.brezillon@collabora.com >>>>>>>> Cc: Tian Tao tiantao6@hisilicon.com >>>>>>>> Cc: Jack Zhang Jack.Zhang1@amd.com >>>>>>>> Cc: etnaviv@lists.freedesktop.org >>>>>>>> Cc: lima@lists.freedesktop.org >>>>>>>> Cc: linux-media@vger.kernel.org >>>>>>>> Cc: linaro-mm-sig@lists.linaro.org >>>>>>>> Cc: Emma Anholt emma@anholt.net >>>>>>>> --- >>>>>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 2 ++ >>>>>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_job.c | 2 ++ >>>>>>>> drivers/gpu/drm/etnaviv/etnaviv_sched.c | 2 ++ >>>>>>>> drivers/gpu/drm/lima/lima_sched.c | 2 ++ >>>>>>>> drivers/gpu/drm/panfrost/panfrost_job.c | 2 ++ >>>>>>>> drivers/gpu/drm/scheduler/sched_entity.c | 6 ++-- >>>>>>>> drivers/gpu/drm/scheduler/sched_fence.c | 17 +++++---- >>>>>>>> drivers/gpu/drm/scheduler/sched_main.c | 46 +++++++++++++++++++++--- >>>>>>>> drivers/gpu/drm/v3d/v3d_gem.c | 2 ++ >>>>>>>> include/drm/gpu_scheduler.h | 7 +++- >>>>>>>> 10 files changed, 74 insertions(+), 14 deletions(-) >>>>>>>> >>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c >>>>>>>> index c5386d13eb4a..a4ec092af9a7 100644 >>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c >>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c >>>>>>>> @@ -1226,6 +1226,8 @@ static int amdgpu_cs_submit(struct amdgpu_cs_parser *p, >>>>>>>> if (r) >>>>>>>> goto error_unlock; >>>>>>>> >>>>>>>> + drm_sched_job_arm(&job->base); >>>>>>>> + >>>>>>>> /* No memory allocation is allowed while holding the notifier lock. >>>>>>>> * The lock is held until amdgpu_cs_submit is finished and fence is >>>>>>>> * added to BOs. >>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c >>>>>>>> index d33e6d97cc89..5ddb955d2315 100644 >>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c >>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c >>>>>>>> @@ -170,6 +170,8 @@ int amdgpu_job_submit(struct amdgpu_job *job, struct drm_sched_entity *entity, >>>>>>>> if (r) >>>>>>>> return r; >>>>>>>> >>>>>>>> + drm_sched_job_arm(&job->base); >>>>>>>> + >>>>>>>> *f = dma_fence_get(&job->base.s_fence->finished); >>>>>>>> amdgpu_job_free_resources(job); >>>>>>>> drm_sched_entity_push_job(&job->base, entity); >>>>>>>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sched.c b/drivers/gpu/drm/etnaviv/etnaviv_sched.c >>>>>>>> index feb6da1b6ceb..05f412204118 100644 >>>>>>>> --- a/drivers/gpu/drm/etnaviv/etnaviv_sched.c >>>>>>>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_sched.c >>>>>>>> @@ -163,6 +163,8 @@ int etnaviv_sched_push_job(struct drm_sched_entity *sched_entity, >>>>>>>> if (ret) >>>>>>>> goto out_unlock; >>>>>>>> >>>>>>>> + drm_sched_job_arm(&submit->sched_job); >>>>>>>> + >>>>>>>> submit->out_fence = dma_fence_get(&submit->sched_job.s_fence->finished); >>>>>>>> submit->out_fence_id = idr_alloc_cyclic(&submit->gpu->fence_idr, >>>>>>>> submit->out_fence, 0, >>>>>>>> diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c >>>>>>>> index dba8329937a3..38f755580507 100644 >>>>>>>> --- a/drivers/gpu/drm/lima/lima_sched.c >>>>>>>> +++ b/drivers/gpu/drm/lima/lima_sched.c >>>>>>>> @@ -129,6 +129,8 @@ int lima_sched_task_init(struct lima_sched_task *task, >>>>>>>> return err; >>>>>>>> } >>>>>>>> >>>>>>>> + drm_sched_job_arm(&task->base); >>>>>>>> + >>>>>>>> task->num_bos = num_bos; >>>>>>>> task->vm = lima_vm_get(vm); >>>>>>>> >>>>>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c >>>>>>>> index 71a72fb50e6b..2992dc85325f 100644 >>>>>>>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c >>>>>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c >>>>>>>> @@ -288,6 +288,8 @@ int panfrost_job_push(struct panfrost_job *job) >>>>>>>> goto unlock; >>>>>>>> } >>>>>>>> >>>>>>>> + drm_sched_job_arm(&job->base); >>>>>>>> + >>>>>>>> job->render_done_fence = dma_fence_get(&job->base.s_fence->finished); >>>>>>>> >>>>>>>> ret = panfrost_acquire_object_fences(job->bos, job->bo_count, >>>>>>>> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c >>>>>>>> index 79554aa4dbb1..f7347c284886 100644 >>>>>>>> --- a/drivers/gpu/drm/scheduler/sched_entity.c >>>>>>>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c >>>>>>>> @@ -485,9 +485,9 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity) >>>>>>>> * @sched_job: job to submit >>>>>>>> * @entity: scheduler entity >>>>>>>> * >>>>>>>> - * Note: To guarantee that the order of insertion to queue matches >>>>>>>> - * the job's fence sequence number this function should be >>>>>>>> - * called with drm_sched_job_init under common lock. >>>>>>>> + * Note: To guarantee that the order of insertion to queue matches the job's >>>>>>>> + * fence sequence number this function should be called with drm_sched_job_arm() >>>>>>>> + * under common lock. >>>>>>>> * >>>>>>>> * Returns 0 for success, negative error code otherwise. >>>>>>>> */ >>>>>>>> diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c >>>>>>>> index 69de2c76731f..c451ee9a30d7 100644 >>>>>>>> --- a/drivers/gpu/drm/scheduler/sched_fence.c >>>>>>>> +++ b/drivers/gpu/drm/scheduler/sched_fence.c >>>>>>>> @@ -90,7 +90,7 @@ static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f) >>>>>>>> * >>>>>>>> * Free up the fence memory after the RCU grace period. >>>>>>>> */ >>>>>>>> -static void drm_sched_fence_free(struct rcu_head *rcu) >>>>>>>> +void drm_sched_fence_free(struct rcu_head *rcu) >>>>>>>> { >>>>>>>> struct dma_fence *f = container_of(rcu, struct dma_fence, rcu); >>>>>>>> struct drm_sched_fence *fence = to_drm_sched_fence(f); >>>>>>>> @@ -152,11 +152,10 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f) >>>>>>>> } >>>>>>>> EXPORT_SYMBOL(to_drm_sched_fence); >>>>>>>> >>>>>>>> -struct drm_sched_fence *drm_sched_fence_create(struct drm_sched_entity *entity, >>>>>>>> - void *owner) >>>>>>>> +struct drm_sched_fence *drm_sched_fence_alloc(struct drm_sched_entity *entity, >>>>>>>> + void *owner) >>>>>>>> { >>>>>>>> struct drm_sched_fence *fence = NULL; >>>>>>>> - unsigned seq; >>>>>>>> >>>>>>>> fence = kmem_cache_zalloc(sched_fence_slab, GFP_KERNEL); >>>>>>>> if (fence == NULL) >>>>>>>> @@ -166,13 +165,19 @@ struct drm_sched_fence *drm_sched_fence_create(struct drm_sched_entity *entity, >>>>>>>> fence->sched = entity->rq->sched; >>>>>>>> spin_lock_init(&fence->lock); >>>>>>>> >>>>>>>> + return fence; >>>>>>>> +} >>>>>>>> + >>>>>>>> +void drm_sched_fence_init(struct drm_sched_fence *fence, >>>>>>>> + struct drm_sched_entity *entity) >>>>>>>> +{ >>>>>>>> + unsigned seq; >>>>>>>> + >>>>>>>> seq = atomic_inc_return(&entity->fence_seq); >>>>>>>> dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled, >>>>>>>> &fence->lock, entity->fence_context, seq); >>>>>>>> dma_fence_init(&fence->finished, &drm_sched_fence_ops_finished, >>>>>>>> &fence->lock, entity->fence_context + 1, seq); >>>>>>>> - >>>>>>>> - return fence; >>>>>>>> } >>>>>>>> >>>>>>>> module_init(drm_sched_fence_slab_init); >>>>>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c >>>>>>>> index 33c414d55fab..5e84e1500c32 100644 >>>>>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c >>>>>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c >>>>>>>> @@ -48,9 +48,11 @@ >>>>>>>> #include <linux/wait.h> >>>>>>>> #include <linux/sched.h> >>>>>>>> #include <linux/completion.h> >>>>>>>> +#include <linux/dma-resv.h> >>>>>>>> #include <uapi/linux/sched/types.h> >>>>>>>> >>>>>>>> #include <drm/drm_print.h> >>>>>>>> +#include <drm/drm_gem.h> >>>>>>>> #include <drm/gpu_scheduler.h> >>>>>>>> #include <drm/spsc_queue.h> >>>>>>>> >>>>>>>> @@ -569,7 +571,6 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs_ext); >>>>>>>> >>>>>>>> /** >>>>>>>> * drm_sched_job_init - init a scheduler job >>>>>>>> - * >>>>>>>> * @job: scheduler job to init >>>>>>>> * @entity: scheduler entity to use >>>>>>>> * @owner: job owner for debugging >>>>>>>> @@ -577,6 +578,9 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs_ext); >>>>>>>> * Refer to drm_sched_entity_push_job() documentation >>>>>>>> * for locking considerations. >>>>>>>> * >>>>>>>> + * Drivers must make sure drm_sched_job_cleanup() if this function returns >>>>>>>> + * successfully, even when @job is aborted before drm_sched_job_arm() is called. >>>>>>>> + * >>>>>>>> * Returns 0 for success, negative error code otherwise. >>>>>>>> */ >>>>>>>> int drm_sched_job_init(struct drm_sched_job *job, >>>>>>>> @@ -594,7 +598,7 @@ int drm_sched_job_init(struct drm_sched_job *job, >>>>>>>> job->sched = sched; >>>>>>>> job->entity = entity; >>>>>>>> job->s_priority = entity->rq - sched->sched_rq; >>>>>>>> - job->s_fence = drm_sched_fence_create(entity, owner); >>>>>>>> + job->s_fence = drm_sched_fence_alloc(entity, owner); >>>>>>>> if (!job->s_fence) >>>>>>>> return -ENOMEM; >>>>>>>> job->id = atomic64_inc_return(&sched->job_id_count); >>>>>>>> @@ -606,13 +610,47 @@ int drm_sched_job_init(struct drm_sched_job *job, >>>>>>>> EXPORT_SYMBOL(drm_sched_job_init); >>>>>>>> >>>>>>>> /** >>>>>>>> - * drm_sched_job_cleanup - clean up scheduler job resources >>>>>>>> + * drm_sched_job_arm - arm a scheduler job for execution >>>>>>>> + * @job: scheduler job to arm >>>>>>>> + * >>>>>>>> + * This arms a scheduler job for execution. Specifically it initializes the >>>>>>>> + * &drm_sched_job.s_fence of @job, so that it can be attached to struct dma_resv >>>>>>>> + * or other places that need to track the completion of this job. >>>>>>>> + * >>>>>>>> + * Refer to drm_sched_entity_push_job() documentation for locking >>>>>>>> + * considerations. >>>>>>>> * >>>>>>>> + * This can only be called if drm_sched_job_init() succeeded. >>>>>>>> + */ >>>>>>>> +void drm_sched_job_arm(struct drm_sched_job *job) >>>>>>>> +{ >>>>>>>> + drm_sched_fence_init(job->s_fence, job->entity); >>>>>>>> +} >>>>>>>> +EXPORT_SYMBOL(drm_sched_job_arm); >>>>>>>> + >>>>>>>> +/** >>>>>>>> + * drm_sched_job_cleanup - clean up scheduler job resources >>>>>>>> * @job: scheduler job to clean up >>>>>>>> + * >>>>>>>> + * Cleans up the resources allocated with drm_sched_job_init(). >>>>>>>> + * >>>>>>>> + * Drivers should call this from their error unwind code if @job is aborted >>>>>>>> + * before drm_sched_job_arm() is called. >>>>>>>> + * >>>>>>>> + * After that point of no return @job is committed to be executed by the >>>>>>>> + * scheduler, and this function should be called from the >>>>>>>> + * &drm_sched_backend_ops.free_job callback. >>>>>>>> */ >>>>>>>> void drm_sched_job_cleanup(struct drm_sched_job *job) >>>>>>>> { >>>>>>>> - dma_fence_put(&job->s_fence->finished); >>>>>>>> + if (!kref_read(&job->s_fence->finished.refcount)) { >>>>>>>> + /* drm_sched_job_arm() has been called */ >>>>>>>> + dma_fence_put(&job->s_fence->finished); >>>>>>>> + } else { >>>>>>>> + /* aborted job before committing to run it */ >>>>>>>> + drm_sched_fence_free(&job->s_fence->finished.rcu); >>>>>>>> + } >>>>>>>> + >>>>>>>> job->s_fence = NULL; >>>>>>>> } >>>>>>>> EXPORT_SYMBOL(drm_sched_job_cleanup); >>>>>>>> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c >>>>>>>> index 4eb354226972..5c3a99027ecd 100644 >>>>>>>> --- a/drivers/gpu/drm/v3d/v3d_gem.c >>>>>>>> +++ b/drivers/gpu/drm/v3d/v3d_gem.c >>>>>>>> @@ -475,6 +475,8 @@ v3d_push_job(struct v3d_file_priv *v3d_priv, >>>>>>>> if (ret) >>>>>>>> return ret; >>>>>>>> >>>>>>>> + drm_sched_job_arm(&job->base); >>>>>>>> + >>>>>>>> job->done_fence = dma_fence_get(&job->base.s_fence->finished); >>>>>>>> >>>>>>>> /* put by scheduler job completion */ >>>>>>>> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h >>>>>>>> index 88ae7f331bb1..83afc3aa8e2f 100644 >>>>>>>> --- a/include/drm/gpu_scheduler.h >>>>>>>> +++ b/include/drm/gpu_scheduler.h >>>>>>>> @@ -348,6 +348,7 @@ void drm_sched_fini(struct drm_gpu_scheduler *sched); >>>>>>>> int drm_sched_job_init(struct drm_sched_job *job, >>>>>>>> struct drm_sched_entity *entity, >>>>>>>> void *owner); >>>>>>>> +void drm_sched_job_arm(struct drm_sched_job *job); >>>>>>>> void drm_sched_entity_modify_sched(struct drm_sched_entity *entity, >>>>>>>> struct drm_gpu_scheduler **sched_list, >>>>>>>> unsigned int num_sched_list); >>>>>>>> @@ -387,8 +388,12 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity, >>>>>>>> enum drm_sched_priority priority); >>>>>>>> bool drm_sched_entity_is_ready(struct drm_sched_entity *entity); >>>>>>>> >>>>>>>> -struct drm_sched_fence *drm_sched_fence_create( >>>>>>>> +struct drm_sched_fence *drm_sched_fence_alloc( >>>>>>>> struct drm_sched_entity *s_entity, void *owner); >>>>>>>> +void drm_sched_fence_init(struct drm_sched_fence *fence, >>>>>>>> + struct drm_sched_entity *entity); >>>>>>>> +void drm_sched_fence_free(struct rcu_head *rcu); >>>>>>>> + >>>>>>>> void drm_sched_fence_scheduled(struct drm_sched_fence *fence); >>>>>>>> void drm_sched_fence_finished(struct drm_sched_fence *fence);
>>>>>>>>
Daniel Vetter Software Engineer, Intel Corporation https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll....
-- Daniel Vetter Software Engineer, Intel Corporation https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll....