drm/i915/execlists: Remove the priority "optimisation"

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@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171024115501.21033-1-chris@chris-wilson.co.uk
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 5b87d5284a8448bb5bf0679231634e6a422502c0..d36e2560743545cef7b32b24adb794e719ca5da2 100644 (file)
--- 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);