drm/i915: Mark semaphores as complete on unsubmit out if payload was started

Avoid charging us for the presumed busywait if the request was preempted
after successfully using semaphores to reduce inter-engine latency.

v2: Bump the priority to reflect the lack of semaphores now required.

References: ca6e56f6 ("drm/i915: Disable semaphore busywaits on saturated systems")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190515130052.4475-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_request.c

@@ -509,6 +509,12 @@ void __i915_request_unsubmit(struct i915_request *request)
 	/* Transfer back from the global per-engine timeline to per-context */
 	move_to_timeline(request, request->timeline);
 
+	/* We've already spun, don't charge on resubmitting. */
+	if (request->sched.semaphores && i915_request_started(request)) {
+		request->sched.attr.priority |= I915_PRIORITY_NOSEMAPHORE;
+		request->sched.semaphores = 0;
+	}
+
 	/*
 	 * We don't need to wake_up any waiters on request->execute, they
 	 * will get woken by any other event or us re-adding this request