block/cfq: cache rightmost rb_node

For the same reasons we already cache the leftmost pointer, apply the same
optimization for rb_last() calls.  Users must explicitly do this as
rb_root_cached only deals with the smallest node.

[dave@stgolabs.net: brain fart #1]
  Link: http://lkml.kernel.org/r/20170731155955.GD21328@linux-80c1.suse
Link: http://lkml.kernel.org/r/20170719014603.19029-18-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9ba5345ebc9a..9f342ef1ad42 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -94,11 +94,13 @@ struct cfq_ttime {
  */
 struct cfq_rb_root {
         struct rb_root_cached rb;
+        struct rb_node *rb_rightmost;
         unsigned count;
         u64 min_vdisktime;
         struct cfq_ttime ttime;
 };
 #define CFQ_RB_ROOT     (struct cfq_rb_root) { .rb = RB_ROOT_CACHED, \
+                        .rb_rightmost = NULL,                        \
                         .ttime = {.last_end_request = ktime_get_ns(),},}
 
 /*
@@ -1180,6 +1182,9 @@ static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
 
 static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
 {
+        if (root->rb_rightmost == n)
+                root->rb_rightmost = rb_prev(n);
+
         rb_erase_cached(n, &root->rb);
         RB_CLEAR_NODE(n);
 
@@ -1236,20 +1241,24 @@ __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
         struct rb_node *parent = NULL;
         struct cfq_group *__cfqg;
         s64 key = cfqg_key(st, cfqg);
-        bool leftmost = true;
+        bool leftmost = true, rightmost = true;
 
         while (*node != NULL) {
                 parent = *node;
                 __cfqg = rb_entry_cfqg(parent);
 
-                if (key < cfqg_key(st, __cfqg))
+                if (key < cfqg_key(st, __cfqg)) {
                         node = &parent->rb_left;
-                else {
+                        rightmost = false;
+                } else {
                         node = &parent->rb_right;
                         leftmost = false;
                 }
         }
 
+        if (rightmost)
+                st->rb_rightmost = &cfqg->rb_node;
+
         rb_link_node(&cfqg->rb_node, parent, node);
         rb_insert_color_cached(&cfqg->rb_node, &st->rb, leftmost);
 }
@@ -1352,7 +1361,7 @@ cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
          * so that groups get lesser vtime based on their weights, so that
          * if group does not loose all if it was not continuously backlogged.
          */
-        n = rb_last(&st->rb.rb_root);
+        n = st->rb_rightmost;
         if (n) {
                 __cfqg = rb_entry_cfqg(n);
                 cfqg->vdisktime = __cfqg->vdisktime +
@@ -2201,7 +2210,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         st = st_for(cfqq->cfqg, cfqq_class(cfqq), cfqq_type(cfqq));
         if (cfq_class_idle(cfqq)) {
                 rb_key = CFQ_IDLE_DELAY;
-                parent = rb_last(&st->rb.rb_root);
+                parent = st->rb_rightmost;
                 if (parent && parent != &cfqq->rb_node) {
                         __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
                         rb_key += __cfqq->rb_key;