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| author | Tejun Heo <tj@kernel.org> | 2012-03-05 13:15:21 -0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2012-03-06 21:27:24 +0100 |
| commit | 9f13ef678efd977487fc0c2e489f17c9a8c67a3e (patch) | |
| tree | e58a2dd153ad24b2ea173d5dfb575c507e1f7589 /block/cfq.h | |
| parent | e8989fae38d9831c72b20375a206a919ca468c52 (diff) | |
| download | blackbird-op-linux-9f13ef678efd977487fc0c2e489f17c9a8c67a3e.tar.gz blackbird-op-linux-9f13ef678efd977487fc0c2e489f17c9a8c67a3e.zip | |
blkcg: use double locking instead of RCU for blkg synchronization
blkgs are chained from both blkcgs and request_queues and thus
subjected to two locks - blkcg->lock and q->queue_lock. As both blkcg
and q can go away anytime, locking during removal is tricky. It's
currently solved by wrapping removal inside RCU, which makes the
synchronization complex. There are three locks to worry about - the
outer RCU, q lock and blkcg lock, and it leads to nasty subtle
complications like conditional synchronize_rcu() on queue exit paths.
For all other paths, blkcg lock is naturally nested inside q lock and
the only exception is blkcg removal path, which is a very cold path
and can be implemented as clumsy but conceptually-simple reverse
double lock dancing.
This patch updates blkg removal path such that blkgs are removed while
holding both q and blkcg locks, which is trivial for request queue
exit path - blkg_destroy_all(). The blkcg removal path,
blkiocg_pre_destroy(), implements reverse double lock dancing
essentially identical to ioc_release_fn().
This simplifies blkg locking - no half-dead blkgs to worry about. Now
unnecessary RCU annotations will be removed by the next patch.
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.h')
| -rw-r--r-- | block/cfq.h | 10 |
1 files changed, 0 insertions, 10 deletions
diff --git a/block/cfq.h b/block/cfq.h index 5584e1b63ca8..c8b15ef57e5d 100644 --- a/block/cfq.h +++ b/block/cfq.h @@ -79,11 +79,6 @@ static inline void cfq_blkiocg_update_completion_stats(struct blkio_group *blkg, direction, sync); } -static inline int cfq_blkiocg_del_blkio_group(struct blkio_group *blkg) -{ - return blkiocg_del_blkio_group(blkg); -} - #else /* CFQ_GROUP_IOSCHED */ static inline void cfq_blkiocg_update_io_add_stats(struct blkio_group *blkg, struct blkio_policy_type *pol, @@ -119,10 +114,5 @@ static inline void cfq_blkiocg_update_completion_stats(struct blkio_group *blkg, struct blkio_policy_type *pol, uint64_t start_time, uint64_t io_start_time, bool direction, bool sync) { } -static inline int cfq_blkiocg_del_blkio_group(struct blkio_group *blkg) -{ - return 0; -} - #endif /* CFQ_GROUP_IOSCHED */ #endif |
