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blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set()

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We have to remove synchronize_rcu() from blk_queue_cleanup(),
otherwise long delay can be caused during lun probe. For removing
it, we have to avoid to iterate the set->tag_list in IO path, eg,
blk_mq_sched_restart().

This patch reverts 5b79413946d (Revert "blk-mq: don't handle
TAG_SHARED in restart"). Given we have fixed enough IO hang issue,
and there isn't any reason to restart all queues in one tags any more,
see the following reasons:

1) blk-mq core can deal with shared-tags case well via blk_mq_get_driver_tag(),
which can wake up queues waiting for driver tag.

2) SCSI is a bit special because it may return BLK_STS_RESOURCE if queue,
target or host is ready, but SCSI built-in restart can cover all these well,
see scsi_end_request(), queue will be rerun after any request initiated from
this host/target is completed.

In my test on scsi_debug(8 luns), this patch may improve IOPS by 20% ~ 30%
when running I/O on these 8 luns concurrently.

Fixes: 705cda97ee ("blk-mq: Make it safe to use RCU to iterate over blk_mq_tag_set.tag_list")
Cc: Omar Sandoval <osandov@fb.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Reported-by: Andrew Jones <drjones@redhat.com>
Tested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2018-06-25 19:31:48 +08:00 committed by Jens Axboe
parent 5815839b3c
commit 97889f9ac2
3 changed files with 7 additions and 90 deletions
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81
block/blk-mq-sched.c
View File

@ -59,29 +59,16 @@ static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return;
if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
struct request_queue *q = hctx->queue;
if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_inc(&q->shared_hctx_restart);
} else
set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}
static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
{
if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
return false;
if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
struct request_queue *q = hctx->queue;
if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_dec(&q->shared_hctx_restart);
} else
return;
clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
return blk_mq_run_hw_queue(hctx, true);
blk_mq_run_hw_queue(hctx, true);
}
/*
@ -380,68 +367,6 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
return false;
}
/**
* list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
* @pos: loop cursor.
* @skip: the list element that will not be examined. Iteration starts at
* @skip->next.
* @head: head of the list to examine. This list must have at least one
* element, namely @skip.
* @member: name of the list_head structure within typeof(*pos).
*/
#define list_for_each_entry_rcu_rr(pos, skip, head, member) \
for ((pos) = (skip); \
(pos = (pos)->member.next != (head) ? list_entry_rcu( \
(pos)->member.next, typeof(*pos), member) : \
list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
(pos) != (skip); )
/*
* Called after a driver tag has been freed to check whether a hctx needs to
* be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
* queues in a round-robin fashion if the tag set of @hctx is shared with other
* hardware queues.
*/
void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
{
struct blk_mq_tags *const tags = hctx->tags;
struct blk_mq_tag_set *const set = hctx->queue->tag_set;
struct request_queue *const queue = hctx->queue, *q;
struct blk_mq_hw_ctx *hctx2;
unsigned int i, j;
if (set->flags & BLK_MQ_F_TAG_SHARED) {
/*
* If this is 0, then we know that no hardware queues
* have RESTART marked. We're done.
*/
if (!atomic_read(&queue->shared_hctx_restart))
return;
rcu_read_lock();
list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
tag_set_list) {
queue_for_each_hw_ctx(q, hctx2, i)
if (hctx2->tags == tags &&
blk_mq_sched_restart_hctx(hctx2))
goto done;
}
j = hctx->queue_num + 1;
for (i = 0; i < queue->nr_hw_queues; i++, j++) {
if (j == queue->nr_hw_queues)
j = 0;
hctx2 = queue->queue_hw_ctx[j];
if (hctx2->tags == tags &&
blk_mq_sched_restart_hctx(hctx2))
break;
}
done:
rcu_read_unlock();
} else {
blk_mq_sched_restart_hctx(hctx);
}
}
void blk_mq_sched_insert_request(struct request *rq, bool at_head,
bool run_queue, bool async)
{

10
block/blk-mq.c
View File

@ -2335,16 +2335,11 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
int i;
queue_for_each_hw_ctx(q, hctx, i) {
if (shared) {
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_inc(&q->shared_hctx_restart);
if (shared)
hctx->flags |= BLK_MQ_F_TAG_SHARED;
} else {
if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
atomic_dec(&q->shared_hctx_restart);
else
hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
}
}
}
static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set,
@ -2374,7 +2369,6 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
blk_mq_update_tag_set_depth(set, false);
}
mutex_unlock(&set->tag_list_lock);
synchronize_rcu();
INIT_LIST_HEAD(&q->tag_set_list);
}

2
include/linux/blkdev.h
View File

@ -442,8 +442,6 @@ struct request_queue {
int nr_rqs[2]; /* # allocated [a]sync rqs */
int nr_rqs_elvpriv; /* # allocated rqs w/ elvpriv */
atomic_t shared_hctx_restart;
struct blk_queue_stats *stats;
struct rq_wb *rq_wb;