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blk-mq: move srcu from blk_mq_hw_ctx to request_queue

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In case of BLK_MQ_F_BLOCKING, per-hctx srcu is used to protect dispatch
critical area. However, this srcu instance stays at the end of hctx, and
it often takes standalone cacheline, often cold.

Inside srcu_read_lock() and srcu_read_unlock(), WRITE is always done on
the indirect percpu variable which is allocated from heap instead of
being embedded, srcu->srcu_idx is read only in srcu_read_lock(). It
doesn't matter if srcu structure stays in hctx or request queue.

So switch to per-request-queue srcu for protecting dispatch, and this
way simplifies quiesce a lot, not mention quiesce is always done on the
request queue wide.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20211203131534.3668411-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2021-12-03 21:15:32 +08:00 • committed by Jens Axboe
parent 2a904d0085
commit 704b914f15
9 changed files with 53 additions and 49 deletions
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9
include/linux/blkdev.h
View file

@ -16,6 +16,7 @@
#include <linux/percpu-refcount.h>
#include <linux/blkzoned.h>
#include <linux/sbitmap.h>
#include <linux/srcu.h>
struct module;
struct request_queue;
@ -373,11 +374,18 @@ struct request_queue {
* devices that do not have multiple independent access ranges.
*/
struct blk_independent_access_ranges *ia_ranges;
/**
* @srcu: Sleepable RCU. Use as lock when type of the request queue
* is blocking (BLK_MQ_F_BLOCKING). Must be the last member
*/
struct srcu_struct srcu[];
};
/* Keep blk_queue_flag_name[] in sync with the definitions below */
#define QUEUE_FLAG_STOPPED 0 /* queue is stopped */
#define QUEUE_FLAG_DYING 1 /* queue being torn down */
#define QUEUE_FLAG_HAS_SRCU 2 /* SRCU is allocated */
#define QUEUE_FLAG_NOMERGES 3 /* disable merge attempts */
#define QUEUE_FLAG_SAME_COMP 4 /* complete on same CPU-group */
#define QUEUE_FLAG_FAIL_IO 5 /* fake timeout */
@ -415,6 +423,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
#define blk_queue_stopped(q) test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
#define blk_queue_dying(q) test_bit(QUEUE_FLAG_DYING, &(q)->queue_flags)
#define blk_queue_has_srcu(q) test_bit(QUEUE_FLAG_HAS_SRCU, &(q)->queue_flags)
#define blk_queue_dead(q) test_bit(QUEUE_FLAG_DEAD, &(q)->queue_flags)
#define blk_queue_init_done(q) test_bit(QUEUE_FLAG_INIT_DONE, &(q)->queue_flags)
#define blk_queue_nomerges(q) test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)