blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set()
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:
parent
5815839b3c
commit
97889f9ac2
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@ -59,29 +59,16 @@ static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
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if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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return;
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if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
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struct request_queue *q = hctx->queue;
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if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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atomic_inc(&q->shared_hctx_restart);
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} else
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set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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}
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static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
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void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
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{
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if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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return false;
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return;
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clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
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struct request_queue *q = hctx->queue;
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if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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atomic_dec(&q->shared_hctx_restart);
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} else
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clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
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return blk_mq_run_hw_queue(hctx, true);
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blk_mq_run_hw_queue(hctx, true);
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}
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/*
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@ -380,68 +367,6 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
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return false;
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}
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/**
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* list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
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* @pos: loop cursor.
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* @skip: the list element that will not be examined. Iteration starts at
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* @skip->next.
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* @head: head of the list to examine. This list must have at least one
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* element, namely @skip.
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* @member: name of the list_head structure within typeof(*pos).
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*/
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#define list_for_each_entry_rcu_rr(pos, skip, head, member) \
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for ((pos) = (skip); \
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(pos = (pos)->member.next != (head) ? list_entry_rcu( \
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(pos)->member.next, typeof(*pos), member) : \
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list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
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(pos) != (skip); )
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/*
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* Called after a driver tag has been freed to check whether a hctx needs to
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* be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
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* queues in a round-robin fashion if the tag set of @hctx is shared with other
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* hardware queues.
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*/
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void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
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{
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struct blk_mq_tags *const tags = hctx->tags;
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struct blk_mq_tag_set *const set = hctx->queue->tag_set;
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struct request_queue *const queue = hctx->queue, *q;
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struct blk_mq_hw_ctx *hctx2;
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unsigned int i, j;
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if (set->flags & BLK_MQ_F_TAG_SHARED) {
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/*
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* If this is 0, then we know that no hardware queues
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* have RESTART marked. We're done.
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*/
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if (!atomic_read(&queue->shared_hctx_restart))
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return;
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rcu_read_lock();
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list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
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tag_set_list) {
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queue_for_each_hw_ctx(q, hctx2, i)
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if (hctx2->tags == tags &&
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blk_mq_sched_restart_hctx(hctx2))
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goto done;
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}
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j = hctx->queue_num + 1;
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for (i = 0; i < queue->nr_hw_queues; i++, j++) {
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if (j == queue->nr_hw_queues)
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j = 0;
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hctx2 = queue->queue_hw_ctx[j];
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if (hctx2->tags == tags &&
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blk_mq_sched_restart_hctx(hctx2))
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break;
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}
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done:
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rcu_read_unlock();
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} else {
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blk_mq_sched_restart_hctx(hctx);
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}
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}
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void blk_mq_sched_insert_request(struct request *rq, bool at_head,
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bool run_queue, bool async)
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{
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@ -2335,15 +2335,10 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
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int i;
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queue_for_each_hw_ctx(q, hctx, i) {
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if (shared) {
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if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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atomic_inc(&q->shared_hctx_restart);
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if (shared)
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hctx->flags |= BLK_MQ_F_TAG_SHARED;
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} else {
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if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
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atomic_dec(&q->shared_hctx_restart);
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else
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hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
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}
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}
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}
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@ -2374,7 +2369,6 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
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blk_mq_update_tag_set_depth(set, false);
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}
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mutex_unlock(&set->tag_list_lock);
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synchronize_rcu();
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INIT_LIST_HEAD(&q->tag_set_list);
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}
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@ -442,8 +442,6 @@ struct request_queue {
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int nr_rqs[2]; /* # allocated [a]sync rqs */
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int nr_rqs_elvpriv; /* # allocated rqs w/ elvpriv */
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atomic_t shared_hctx_restart;
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struct blk_queue_stats *stats;
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struct rq_wb *rq_wb;
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