drm/i915: Defer kicking the tasklet until all rescheduling is complete

Since we may kick more than engine, and may kick each one a couple of
times, coalesce the tasklet execution to the end. This also ensures that
we have the chance to run the tasklet immediately after priority
bumping.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200331114852.11583-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_scheduler.c

@@ -464,11 +464,15 @@ int i915_sched_node_add_dependency(struct i915_sched_node *node,
 	if (!dep)
 		return -ENOMEM;
 
+	local_bh_disable();
+
 	if (!__i915_sched_node_add_dependency(node, signal, dep,
 					      I915_DEPENDENCY_EXTERNAL |
 					      I915_DEPENDENCY_ALLOC))
 		i915_dependency_free(dep);
 
+	local_bh_enable(); /* kick submission tasklet */
+
 	return 0;
 }