linux/block/cfq.h
Tejun Heo 9f13ef678e 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>
2012-03-06 21:27:24 +01:00

119 lines
4.0 KiB
C

#ifndef _CFQ_H
#define _CFQ_H
#include "blk-cgroup.h"
#ifdef CONFIG_CFQ_GROUP_IOSCHED
static inline void cfq_blkiocg_update_io_add_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol,
struct blkio_group *curr_blkg,
bool direction, bool sync)
{
blkiocg_update_io_add_stats(blkg, pol, curr_blkg, direction, sync);
}
static inline void cfq_blkiocg_update_dequeue_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, unsigned long dequeue)
{
blkiocg_update_dequeue_stats(blkg, pol, dequeue);
}
static inline void cfq_blkiocg_update_timeslice_used(struct blkio_group *blkg,
struct blkio_policy_type *pol, unsigned long time,
unsigned long unaccounted_time)
{
blkiocg_update_timeslice_used(blkg, pol, time, unaccounted_time);
}
static inline void cfq_blkiocg_set_start_empty_time(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
blkiocg_set_start_empty_time(blkg, pol);
}
static inline void cfq_blkiocg_update_io_remove_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, bool direction,
bool sync)
{
blkiocg_update_io_remove_stats(blkg, pol, direction, sync);
}
static inline void cfq_blkiocg_update_io_merged_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, bool direction,
bool sync)
{
blkiocg_update_io_merged_stats(blkg, pol, direction, sync);
}
static inline void cfq_blkiocg_update_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
blkiocg_update_idle_time_stats(blkg, pol);
}
static inline void
cfq_blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
blkiocg_update_avg_queue_size_stats(blkg, pol);
}
static inline void
cfq_blkiocg_update_set_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol)
{
blkiocg_update_set_idle_time_stats(blkg, pol);
}
static inline void cfq_blkiocg_update_dispatch_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, uint64_t bytes,
bool direction, bool sync)
{
blkiocg_update_dispatch_stats(blkg, pol, bytes, direction, sync);
}
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)
{
blkiocg_update_completion_stats(blkg, pol, start_time, io_start_time,
direction, sync);
}
#else /* CFQ_GROUP_IOSCHED */
static inline void cfq_blkiocg_update_io_add_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol,
struct blkio_group *curr_blkg, bool direction,
bool sync) { }
static inline void cfq_blkiocg_update_dequeue_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, unsigned long dequeue) { }
static inline void cfq_blkiocg_update_timeslice_used(struct blkio_group *blkg,
struct blkio_policy_type *pol, unsigned long time,
unsigned long unaccounted_time) { }
static inline void cfq_blkiocg_set_start_empty_time(struct blkio_group *blkg,
struct blkio_policy_type *pol) { }
static inline void cfq_blkiocg_update_io_remove_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, bool direction,
bool sync) { }
static inline void cfq_blkiocg_update_io_merged_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, bool direction,
bool sync) { }
static inline void cfq_blkiocg_update_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol) { }
static inline void
cfq_blkiocg_update_avg_queue_size_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol) { }
static inline void
cfq_blkiocg_update_set_idle_time_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol) { }
static inline void cfq_blkiocg_update_dispatch_stats(struct blkio_group *blkg,
struct blkio_policy_type *pol, uint64_t bytes,
bool direction, bool sync) { }
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) { }
#endif /* CFQ_GROUP_IOSCHED */
#endif