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authorTejun Heo <tj@kernel.org>2012-03-05 13:15:22 -0800
committerJens Axboe <axboe@kernel.dk>2012-03-06 21:27:24 +0100
commitc875f4d0250a1f070fa26087a73bdd8f54c48100 (patch)
tree4ed2bae2fc48e54ac712d28eaaae8217c8064c1d /block/cfq-iosched.c
parent9f13ef678efd977487fc0c2e489f17c9a8c67a3e (diff)
downloadlinux-c875f4d0250a1f070fa26087a73bdd8f54c48100.tar.bz2
blkcg: drop unnecessary RCU locking
Now that blkg additions / removals are always done under both q and blkcg locks, the only places RCU locking is necessary are blkg_lookup[_create]() for lookup w/o blkcg lock. This patch drops unncessary RCU locking replacing it with plain blkcg locking as necessary. * blkiocg_pre_destroy() already perform proper locking and don't need RCU. Dropped. * blkio_read_blkg_stats() now uses blkcg->lock instead of RCU read lock. This isn't a hot path. * Now unnecessary synchronize_rcu() from queue exit paths removed. This makes q->nr_blkgs unnecessary. Dropped. * RCU annotation on blkg->q removed. -v2: Vivek pointed out that blkg_lookup_create() still needs to be called under rcu_read_lock(). Updated. -v3: After the update, stats_lock locking in blkio_read_blkg_stats() shouldn't be using _irq variant as it otherwise ends up enabling irq while blkcg->lock is locked. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/cfq-iosched.c')
-rw-r--r--block/cfq-iosched.c24
1 files changed, 0 insertions, 24 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 393eaa59913b..9e386d9bcb79 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3449,7 +3449,6 @@ static void cfq_exit_queue(struct elevator_queue *e)
{
struct cfq_data *cfqd = e->elevator_data;
struct request_queue *q = cfqd->queue;
- bool wait = false;
cfq_shutdown_timer_wq(cfqd);
@@ -3462,31 +3461,8 @@ static void cfq_exit_queue(struct elevator_queue *e)
spin_unlock_irq(q->queue_lock);
-#ifdef CONFIG_BLK_CGROUP
- /*
- * If there are groups which we could not unlink from blkcg list,
- * wait for a rcu period for them to be freed.
- */
- spin_lock_irq(q->queue_lock);
- wait = q->nr_blkgs;
- spin_unlock_irq(q->queue_lock);
-#endif
cfq_shutdown_timer_wq(cfqd);
- /*
- * Wait for cfqg->blkg->key accessors to exit their grace periods.
- * Do this wait only if there are other unlinked groups out
- * there. This can happen if cgroup deletion path claimed the
- * responsibility of cleaning up a group before queue cleanup code
- * get to the group.
- *
- * Do not call synchronize_rcu() unconditionally as there are drivers
- * which create/delete request queue hundreds of times during scan/boot
- * and synchronize_rcu() can take significant time and slow down boot.
- */
- if (wait)
- synchronize_rcu();
-
#ifndef CONFIG_CFQ_GROUP_IOSCHED
kfree(cfqd->root_group);
#endif