[Intel-gfx] [RFC 2/4] drm/i915/scheduler: Make insert_request resubmission aware

[Michał Winiarski]

Normally when we're inserting requests with equal priority, we're using
FIFO ordering. However, when we're resubmitting requests it's helpful
to be able to ensure that they're executed before their dependencies,
meaning that we need to use LIFO ordering instead.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski at intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 301ae7c..107cf91 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -611,12 +611,15 @@ static void intel_lrc_irq_handler(unsigned long data)
 	intel_uncore_forcewake_put(dev_priv, engine->fw_domains);
 }
 
-static bool insert_request(struct i915_priotree *pt, struct rb_root *root)
+static bool insert_request(struct i915_priotree *pt, struct rb_root *root,
+			   bool reinsert)
 {
 	struct rb_node **p, *rb;
 	bool first = true;
 
-	/* most positive priority is scheduled first, equal priorities fifo */
+	/* most positive priority is scheduled first,
+	 * equal priorities - fifo, except when we're reinserting - lifo
+	 */
 	rb = NULL;
 	p = &root->rb_node;
 	while (*p) {
@@ -624,7 +627,8 @@ static bool insert_request(struct i915_priotree *pt, struct rb_root *root)
 
 		rb = *p;
 		pos = rb_entry(rb, typeof(*pos), node);
-		if (pt->priority > pos->priority) {
+		if ((pt->priority > pos->priority) ||
+		    ((pt->priority == pos->priority) && reinsert)) {
 			p = &rb->rb_left;
 		} else {
 			p = &rb->rb_right;
@@ -645,7 +649,8 @@ static void execlists_submit_request(struct drm_i915_gem_request *request)
 	/* Will be called from irq-context when using foreign fences. */
 	spin_lock_irqsave(&engine->timeline->lock, flags);
 
-	if (insert_request(&request->priotree, &engine->execlist_queue)) {
+	if (insert_request(&request->priotree,
+			   &engine->execlist_queue, false)) {
 		engine->execlist_first = &request->priotree.node;
 		if (execlists_elsp_ready(engine))
 			tasklet_hi_schedule(&engine->irq_tasklet);
@@ -742,7 +747,7 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
 
 		pt->priority = prio;
 		rb_erase(&pt->node, &engine->execlist_queue);
-		if (insert_request(pt, &engine->execlist_queue))
+		if (insert_request(pt, &engine->execlist_queue, false))
 			engine->execlist_first = &pt->node;
 	}
 
-- 
2.9.3