[Intel-gfx] [PATCH] drm/i915/execlists: Remove the priority "optimisation"

[Michał Winiarski]

On Tue, Oct 24, 2017 at 12:55:01PM +0100, Chris Wilson wrote:
> Originally we set the priority to max upon inserting the request into
> the execlists queue (and removing it from the scheduler lists). We could
> then use the prio==INT_MAX as a shortcut within execlists_schedule() to
> detect the end of the dependency chain. Since commit 1f181225f8ec
> ("drm/i915/execlists: Keep request->priority for its lifetime") this is
> no longer true as we use the request completion as an indicator the
> schedule dependency chain is complete instead. (This allows us to then
> reschedule requests even when its context is in flight.) However, this
> makes the GEM_BUG_ON() inside execlists_schedule() racy as we may change
> the rq->prio at the same time. As the assertion is useful, let's keep
> the assertion and remove the micro-optimisation.
> 
> Fixes: 1f181225f8ec ("drm/i915/execlists: Keep request->priority for its lifetime")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Reviewed-by: Michał Winiarski <michal.winiarski at intel.com>

-Michał

> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 233c992a886b..c63960fee102 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -734,7 +734,6 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
>  
>  		list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
>  			INIT_LIST_HEAD(&rq->priotree.link);
> -			rq->priotree.priority = INT_MAX;
>  
>  			dma_fence_set_error(&rq->fence, -EIO);
>  			__i915_gem_request_submit(rq);
> @@ -891,7 +890,6 @@ static void intel_lrc_irq_handler(unsigned long data)
>  				execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
>  
>  				trace_i915_gem_request_out(rq);
> -				rq->priotree.priority = INT_MAX;
>  				i915_gem_request_put(rq);
>  
>  				execlists_port_complete(execlists, port);
> -- 
> 2.15.0.rc1
>