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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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8
include/linux/blk-mq.h
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@@ -4,7 +4,6 @@
#include <linux/blkdev.h>
#include <linux/sbitmap.h>
#include <linux/srcu.h>
#include <linux/lockdep.h>
#include <linux/scatterlist.h>
#include <linux/prefetch.h>
@@ -375,13 +374,6 @@ struct blk_mq_hw_ctx {
* q->unused_hctx_list.
*/
struct list_head hctx_list;
/**
* @srcu: Sleepable RCU. Use as lock when type of the hardware queue is
* blocking (BLK_MQ_F_BLOCKING). Must be the last member - see also
* blk_mq_hw_ctx_size().
*/
struct srcu_struct srcu[];
};
/**