blkcg: move root blkg lookup optimization from throtl_lookup_tg() to __blkg_lookup()

htejun · axboe · commit 85b6bc9db6d5 · 2015-08-18T15:49:17.000-07:00
Currently, both throttle and cfq policies implement their own root
blkg (blkcg_gq) lookup fast path.  This patch moves root blkg
optimization from throtl_lookup_tg() to __blkg_lookup().  cfq-iosched
currently doesn't use blkg_lookup() but will be converted and drop the
optimization too.

Signed-off-by: Tejun Heo &lt;tj@kernel.org&gt;
Cc: Vivek Goyal &lt;vgoyal@redhat.com&gt;
Cc: Arianna Avanzini &lt;avanzini.arianna@gmail.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@fb.com&gt;
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
@@ -452,13 +452,6 @@ static void throtl_pd_reset_stats(struct blkg_policy_data *pd)
 static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td,
 					   struct blkcg *blkcg)
 {
-	/*
-	 * This is the common case when there are no blkcgs.  Avoid lookup
-	 * in this case
-	 */
-	if (blkcg == &blkcg_root)
-		return td_root_tg(td);
-
 	return blkg_to_tg(blkg_lookup(blkcg, td->queue));
 }
 
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
@@ -249,6 +249,9 @@ static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
 {
 	struct blkcg_gq *blkg;
 
+	if (blkcg == &blkcg_root)
+		return q->root_blkg;
+
 	blkg = rcu_dereference(blkcg->blkg_hint);
 	if (blkg && blkg->q == q)
 		return blkg;

Original file line number	Diff line number	Diff line change
`@@ -452,13 +452,6 @@ static void throtl_pd_reset_stats(struct blkg_policy_data *pd)`
`452`	`452`	`static struct throtl_grp throtl_lookup_tg(struct throtl_data td,`
`453`	`453`	`struct blkcg *blkcg)`
`454`	`454`	`{`
`455`		`- /*`
`456`		`- * This is the common case when there are no blkcgs. Avoid lookup`
`457`		`- * in this case`
`458`		`- */`
`459`		`- if (blkcg == &blkcg_root)`
`460`		`- return td_root_tg(td);`
`461`		`-`
`462`	`455`	`return blkg_to_tg(blkg_lookup(blkcg, td->queue));`
`463`	`456`	`}`
`464`	`457`
Original file line number	Diff line number	Diff line change
`@@ -249,6 +249,9 @@ static inline struct blkcg_gq __blkg_lookup(struct blkcg blkcg,`
`249`	`249`	`{`
`250`	`250`	`struct blkcg_gq *blkg;`
`251`	`251`
	`252`	`+ if (blkcg == &blkcg_root)`
	`253`	`+ return q->root_blkg;`
	`254`	`+`
`252`	`255`	`blkg = rcu_dereference(blkcg->blkg_hint);`
`253`	`256`	`if (blkg && blkg->q == q)`
`254`	`257`	`return blkg;`