cfq-iosched: sort RT queues into the rbtree

Currently CFQ does a linked insert into the current list for RT
queues. We can just factor the class into the rb insertion,
and then we don't have to treat RT queues in a special way. It's
faster, too.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 55c476baa692f4127e15c9c50562aa93699cbe0b..81c057eadfccd5f5c9480e0fa752a49d566bbcb7 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -471,7 +471,16 @@ static void cfq_service_tree_add(struct cfq_data *cfqd,
                parent = *p;
                __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
 
-               if (rb_key < __cfqq->rb_key)
+               /*
+                * sort RT queues first, we always want to give
+                * preference to them. after that, sort on the next
+                * service time.
+                */
+               if (cfq_class_rt(cfqq) > cfq_class_rt(__cfqq))
+                       p = &(*p)->rb_left;
+               else if (cfq_class_rt(cfqq) < cfq_class_rt(__cfqq))
+                       p = &(*p)->rb_right;
+               else if (rb_key < __cfqq->rb_key)
                        p = &(*p)->rb_left;
                else {
                        p = &(*p)->rb_right;
@@ -490,7 +499,6 @@ static void cfq_service_tree_add(struct cfq_data *cfqd,
 static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
 {
        struct cfq_data *cfqd = cfqq->cfqd;
-       struct list_head *n;
 
        /*
         * Resorting requires the cfqq to be on the RR list already.
@@ -500,25 +508,14 @@ static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
 
        list_del_init(&cfqq->cfq_list);
 
-       if (cfq_class_rt(cfqq)) {
-               /*
-                * At to the front of the current list, but behind other
-                * RT queues.
-                */
-               n = &cfqd->cur_rr;
-               while (n->next != &cfqd->cur_rr)
-                       if (!cfq_class_rt(cfqq))
-                               break;
-
-               list_add(&cfqq->cfq_list, n);
-       } else if (cfq_class_idle(cfqq)) {
+       if (cfq_class_idle(cfqq)) {
                /*
                 * IDLE goes to the tail of the idle list
                 */
                list_add_tail(&cfqq->cfq_list, &cfqd->idle_rr);
        } else {
                /*
-                * So we get here, ergo the queue is a regular best-effort queue
+                * RT and BE queues, sort into the rbtree
                 */
                cfq_service_tree_add(cfqd, cfqq);
        }