[PATCH 03/10] blkcg: move root blkg lookup optimization from throtl_lookup_tg() to __blkg_lookup()

Tejun Heo
2015-07-12T18:02:49Z

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 <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
---
block/blk-throttle.c | 7 -------
include/linux/blk-cgroup.h | 3 +++
2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index c2c7547..1f63fc8 100644
--- 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
index d5b54aa..0609bce 100644
--- 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;
--
2.4.3