cfq-iosched: speedup cic rb lookup

We often lookup the same queue many times in succession, so cache
the last looked up queue to avoid browsing the rbtree.

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

1 files changed, 18 insertions, 2 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 94f53a1f4677..64df3fa303b0 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1165,6 +1165,8 @@ static void cfq_free_io_context(struct io_context *ioc)
         struct rb_node *n;
         int freed = 0;
 
+        ioc->ioc_data = NULL;
+
         while ((n = rb_first(&ioc->cic_root)) != NULL) {
                 __cic = rb_entry(n, struct cfq_io_context, rb_node);
                 rb_erase(&__cic->rb_node, &ioc->cic_root);
@@ -1228,10 +1230,11 @@ static void cfq_exit_io_context(struct io_context *ioc)
         struct cfq_io_context *__cic;
         struct rb_node *n;
 
+        ioc->ioc_data = NULL;
+
         /*
          * put the reference this task is holding to the various queues
          */
-
         n = rb_first(&ioc->cic_root);
         while (n != NULL) {
                 __cic = rb_entry(n, struct cfq_io_context, rb_node);
@@ -1415,6 +1418,10 @@ static void
 cfq_drop_dead_cic(struct io_context *ioc, struct cfq_io_context *cic)
 {
         WARN_ON(!list_empty(&cic->queue_list));
+
+        if (ioc->ioc_data == cic)
+                ioc->ioc_data = NULL;
+
         rb_erase(&cic->rb_node, &ioc->cic_root);
         kmem_cache_free(cfq_ioc_pool, cic);
         elv_ioc_count_dec(ioc_count);
@@ -1430,6 +1437,13 @@ cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)
         if (unlikely(!ioc))
                 return NULL;
 
+        /*
+         * we maintain a last-hit cache, to avoid browsing over the tree
+         */
+        cic = ioc->ioc_data;
+        if (cic && cic->key == cfqd)
+                return cic;
+
 restart:
         n = ioc->cic_root.rb_node;
         while (n) {
@@ -1445,8 +1459,10 @@ restart:
                         n = n->rb_left;
                 else if (key > k)
                         n = n->rb_right;
-                else
+                else {
+                        ioc->ioc_data = cic;
                         return cic;
+                }
         }
 
         return NULL;