drm/i915: Check for no-op priority changes first

In all likelihood, the priority and node are already in the CPU cache
and by checking them first, we can avoid having to chase the
*request->hwsp for the current breadcrumb.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190513120102.29660-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_scheduler.c

@@ -200,10 +200,10 @@ static void __i915_schedule(struct i915_sched_node *node,
 	lockdep_assert_held(&schedule_lock);
 	GEM_BUG_ON(prio == I915_PRIORITY_INVALID);
 
-	if (node_signaled(node))
+	if (prio <= READ_ONCE(node->attr.priority))
 		return;
 
-	if (prio <= READ_ONCE(node->attr.priority))
+	if (node_signaled(node))
 		return;
 
 	stack.signaler = node;