[Mesa-dev] [PATCH 4/6] gallium: add way for drivers to create fences without flushing

[Rob Clark]

well,

https://groups.google.com/a/chromium.org/forum/#!topic/chromium-os-reviews/IFiv8rZfAq0

does imply that it could be called without a ctx bound..  hmm..

BR,
-R

On Mon, Apr 4, 2016 at 8:43 AM, Rob Clark <robdclark at gmail.com> wrote:
> Hmm, what are the requirements of eglClientWaitSyncKHR() about having
> current context bound?  Not being thread-safe (ie. being associated w/
> current ctx) is pretty important to allow apps that create fences at
> in-opportune times to not force a mid-frame flush for tilers.. :-(
>
> BR,
> -R
>
>
> On Mon, Apr 4, 2016 at 8:10 AM, Marek Olšák <maraeo at gmail.com> wrote:
>> There is one problem with this: It doesn't allow calling
>> pipe_context::fence_finish from another thread in a thread-safe
>> manner, and it implies that fence_finish is generally NOT thread-safe.
>> This thread safety is something I'd like to preserve.
>>
>> I would say that a flush flag telling the driver not to flush would be
>> better, so that drivers which have per-screen fences and cheap flushes
>> can ignore it.
>>
>> Marek
>>
>> On Fri, Apr 1, 2016 at 10:29 PM, Rob Clark <robdclark at gmail.com> wrote:
>>> From: Rob Clark <robclark at freedesktop.org>
>>>
>>> Since current thing is kinda horrible for tilers.  And that issue will
>>> be even worse with EGL_ANDROID_native_fence_sync.
>>>
>>> Not wired up yet for gl syncobj, which can come later.  For now we just
>>> need this with EGL.
>>>
>>> Signed-off-by: Rob Clark <robclark at freedesktop.org>
>>> ---
>>>  src/gallium/include/pipe/p_context.h  | 24 ++++++++++++++++++++++++
>>>  src/gallium/state_trackers/dri/dri2.c | 29 ++++++++++++++++++++---------
>>>  2 files changed, 44 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/src/gallium/include/pipe/p_context.h b/src/gallium/include/pipe/p_context.h
>>> index 1c97e82..02a946b 100644
>>> --- a/src/gallium/include/pipe/p_context.h
>>> +++ b/src/gallium/include/pipe/p_context.h
>>> @@ -457,6 +457,30 @@ struct pipe_context {
>>>                   unsigned flags);
>>>
>>>     /**
>>> +    * Create a fence without necessarily flushing rendering.  Note
>>> +    * that if the driver implements this, it must also implement
>>> +    * ctx->fence_finish() which will be used instead of
>>> +    * screen->fence_finish() to give the driver an opportunity to
>>> +    * flush.
>>> +    *
>>> +    * This allows drivers, in particular tilers, to defer flush
>>> +    * until someone actually wants to wait on a fence.
>>> +    *
>>> +    * \param fence  if not NULL, an old fence to unref and transfer a
>>> +    *    new fence reference to
>>> +    */
>>> +   void (*create_fence)(struct pipe_context *pipe,
>>> +                        struct pipe_fence_handle **fence);
>>> +
>>> +   /**
>>> +    * Wait for the fence to finish.
>>> +    * \param timeout in nanoseconds (may be PIPE_TIMEOUT_INFINITE).
>>> +    */
>>> +   boolean (*fence_finish)(struct pipe_context *pipe,
>>> +                           struct pipe_fence_handle *fence,
>>> +                           uint64_t timeout);
>>> +
>>> +   /**
>>>      * Create a view on a texture to be used by a shader stage.
>>>      */
>>>     struct pipe_sampler_view * (*create_sampler_view)(struct pipe_context *ctx,
>>> diff --git a/src/gallium/state_trackers/dri/dri2.c b/src/gallium/state_trackers/dri/dri2.c
>>> index fb0a180..b66d885 100644
>>> --- a/src/gallium/state_trackers/dri/dri2.c
>>> +++ b/src/gallium/state_trackers/dri/dri2.c
>>> @@ -1320,7 +1320,12 @@ dri2_create_fence(__DRIcontext *_ctx)
>>>     if (!fence)
>>>        return NULL;
>>>
>>> -   ctx->flush(ctx, &fence->pipe_fence, 0);
>>> +   if (ctx->create_fence) {
>>> +      debug_assert(ctx->fence_finish);
>>> +      ctx->create_fence(ctx, &fence->pipe_fence);
>>> +   } else {
>>> +      ctx->flush(ctx, &fence->pipe_fence, 0);
>>> +   }
>>>
>>>     if (!fence->pipe_fence) {
>>>        FREE(fence);
>>> @@ -1376,27 +1381,33 @@ static GLboolean
>>>  dri2_client_wait_sync(__DRIcontext *_ctx, void *_fence, unsigned flags,
>>>                        uint64_t timeout)
>>>  {
>>> +   struct pipe_context *ctx = dri_context(_ctx)->st->pipe;
>>>     struct dri2_fence *fence = (struct dri2_fence*)_fence;
>>>     struct dri_screen *driscreen = fence->driscreen;
>>>     struct pipe_screen *screen = driscreen->base.screen;
>>> +   struct pipe_fence_handle *pipe_fence = NULL;
>>>
>>> -   /* No need to flush. The context was flushed when the fence was created. */
>>> +   /* No need to flush. The context was flushed when the fence was created,
>>> +    * or the ctx implements ctx->fence_finish() which will take care of
>>> +    * flushing if required
>>> +    */
>>>
>>>     if (fence->pipe_fence)
>>> -      return screen->fence_finish(screen, fence->pipe_fence, timeout);
>>> +      pipe_fence = fence->pipe_fence;
>>>     else if (fence->cl_event) {
>>> -      struct pipe_fence_handle *pipe_fence =
>>> -         driscreen->opencl_dri_event_get_fence(fence->cl_event);
>>> -
>>> -      if (pipe_fence)
>>> -         return screen->fence_finish(screen, pipe_fence, timeout);
>>> -      else
>>> +      pipe_fence = driscreen->opencl_dri_event_get_fence(fence->cl_event);
>>> +      if (!pipe_fence)
>>>           return driscreen->opencl_dri_event_wait(fence->cl_event, timeout);
>>>     }
>>>     else {
>>>        assert(0);
>>>        return false;
>>>     }
>>> +
>>> +   if (ctx->fence_finish)
>>> +      return ctx->fence_finish(ctx, pipe_fence, timeout);
>>> +
>>> +   return screen->fence_finish(screen, pipe_fence, timeout);
>>>  }
>>>
>>>  static void
>>> --
>>> 2.5.5
>>>
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