From c875f4d0250a1f070fa26087a73bdd8f54c48100 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 5 Mar 2012 13:15:22 -0800 Subject: 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 Cc: Vivek Goyal Signed-off-by: Jens Axboe --- block/blk-throttle.c | 33 +-------------------------------- 1 file changed, 1 insertion(+), 32 deletions(-) (limited to 'block/blk-throttle.c') diff --git a/block/blk-throttle.c b/block/blk-throttle.c index e35ee7aeea6..bfa5168249e 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -1046,39 +1046,8 @@ int blk_throtl_init(struct request_queue *q) void blk_throtl_exit(struct request_queue *q) { - struct throtl_data *td = q->td; - bool wait; - - BUG_ON(!td); - + BUG_ON(!q->td); throtl_shutdown_wq(q); - - /* If there are other groups */ - spin_lock_irq(q->queue_lock); - wait = q->nr_blkgs; - spin_unlock_irq(q->queue_lock); - - /* - * Wait for tg_to_blkg(tg)->q accessors to exit their grace periods. - * Do this wait only if there are other undestroyed groups out - * there (other than root group). 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(); - - /* - * Just being safe to make sure after previous flush if some body did - * update limits through cgroup and another work got queued, cancel - * it. - */ - throtl_shutdown_wq(q); - kfree(q->td); } -- cgit v1.2.3