On Fri, Mar 17, 2017 at 11:27:22AM +0000, Chris Wilson wrote:
> Do an early read of the execlists' queue before we take the spinlock and
> start checking. This is safe as the first writer to the execlists queue
> will cause the tasklet to be run again after a memory barrier.
>
> v2: Keep guc in sync with execlists queue changes
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> Reviewed-by: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_guc_submission.c | 4 ++++
> drivers/gpu/drm/i915/intel_lrc.c | 4 ++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index a3636b31ebc3..78718a8e70c3 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -577,6 +577,10 @@ static bool i915_guc_dequeue(struct intel_engine_cs *engine)
> struct rb_node *rb;
> bool submit = false;
>
> + /* After execlist_first is updated, a new tasklet must be scheduled */
Hmm, I think this comment is litlle misleading when placed right to the "if" that do early return.
Either extend it with the info from the commit message, or move down.
-Michal
> + if (!READ_ONCE(engine->execlist_first))
> + return false;
> +
> spin_lock_irqsave(&engine->timeline->lock, flags);
> rb = engine->execlist_first;
> while (rb) {
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index becde55b02a3..7adc588d1a19 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -403,6 +403,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> struct rb_node *rb;
> bool submit = false;
>
> + /* After execlist_first is updated, a new tasklet must be scheduled */
> + if (!READ_ONCE(engine->execlist_first))
> + return;
> +
> last = port->request;
> if (last)
> /* WaIdleLiteRestore:bdw,skl
> --
> 2.11.0
>
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