On 06/04/2018 21:17, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-04-05 13:39:19)
From: Tvrtko Ursulin <tvrtko.ursu...@intel.com>

Keep a count of requests submitted from userspace and not yet runnable due
unresolved dependencies.

v2: Rename and move under the container struct. (Chris Wilson)
v3: Rebase.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
  drivers/gpu/drm/i915/i915_request.c     | 3 +++
  drivers/gpu/drm/i915/intel_engine_cs.c  | 3 ++-
  drivers/gpu/drm/i915/intel_ringbuffer.h | 8 ++++++++
  3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c 
index 5c01291ad1cc..152321655fe6 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -640,6 +640,7 @@ submit_notify(struct i915_sw_fence *fence, enum 
i915_sw_fence_notify state)
+               atomic_dec(&request->engine->request_stats.queued);

But we use atomic here? Might as well use atomic for
request_stats.runnable here as well?

I admit it can read a bit uneven.

For runnable I wanted to avoid another atomic by putting it under the engine timeline lock.

But for queued I did not want to start taking the same lock when adding a request.

Your proposal to make runnable atomic_t and move to submit_notify would indeed simplify things, but at a cost of one more atomic in that path. Perhaps the code path is heavy enough for one new atomic to be completely hidden in it, and code simplification to win?



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