blk-throttle: Make dispatch stats per cpu

Currently we take blkg_stat lock for even updating the stats. So even if
a group has no throttling rules (common case for root group), we end
up taking blkg_lock, for updating the stats.

Make dispatch stats per cpu so that these can be updated without taking
blkg lock.

If cpu goes offline, these stats simply disappear. No protection has
been provided for that yet. Do we really need anything for that?

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 606020fe93f..d646b279c8b 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1051,7 +1051,7 @@ static void cfq_init_add_cfqg_lists(struct cfq_data *cfqd,
 static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
 {
 	struct cfq_group *cfqg = NULL;
-	int i, j;
+	int i, j, ret;
 	struct cfq_rb_root *st;
 
 	cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
@@ -1069,6 +1069,13 @@ static struct cfq_group * cfq_alloc_cfqg(struct cfq_data *cfqd)
 	 * or cgroup deletion path depending on who is exiting first.
 	 */
 	cfqg->ref = 1;
+
+	ret = blkio_alloc_blkg_stats(&cfqg->blkg);
+	if (ret) {
+		kfree(cfqg);
+		return NULL;
+	}
+
 	return cfqg;
 }
 
@@ -1183,6 +1190,7 @@ static void cfq_put_cfqg(struct cfq_group *cfqg)
 		return;
 	for_each_cfqg_st(cfqg, i, j, st)
 		BUG_ON(!RB_EMPTY_ROOT(&st->rb));
+	free_percpu(cfqg->blkg.stats_cpu);
 	kfree(cfqg);
 }
 
@@ -3995,7 +4003,15 @@ static void *cfq_init_queue(struct request_queue *q)
 	 * throtl_data goes away.
 	 */
 	cfqg->ref = 2;
+
+	if (blkio_alloc_blkg_stats(&cfqg->blkg)) {
+		kfree(cfqg);
+		kfree(cfqd);
+		return NULL;
+	}
+
 	rcu_read_lock();
+
 	cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
 					(void *)cfqd, 0);
 	rcu_read_unlock();