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 
b/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)
                 rcu_read_lock();
                 request->engine->submit_request(request);
                 rcu_read_unlock();
+               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?

Regards,

Tvrtko


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