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| author | Ming Lei <ming.lei@redhat.com> | 2018-06-25 13:31:49 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-07-09 17:07:52 +0200 |
| commit | 1311326cf4755c7ffefd20f576144ecf46d9906b (patch) | |
| tree | 9f973618b2b1d61520c37a16dbb1d27399f48632 /block | |
| parent | blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set() (diff) | |
| download | linux-1311326cf4755c7ffefd20f576144ecf46d9906b.tar.xz linux-1311326cf4755c7ffefd20f576144ecf46d9906b.zip | |
blk-mq: avoid to synchronize rcu inside blk_cleanup_queue()
SCSI probing may synchronously create and destroy a lot of request_queues
for non-existent devices. Any synchronize_rcu() in queue creation or
destroy path may introduce long latency during booting, see detailed
description in comment of blk_register_queue().
This patch removes one synchronize_rcu() inside blk_cleanup_queue()
for this case, commit c2856ae2f315d75(blk-mq: quiesce queue before freeing queue)
needs synchronize_rcu() for implementing blk_mq_quiesce_queue(), but
when queue isn't initialized, it isn't necessary to do that since
only pass-through requests are involved, no original issue in
scsi_execute() at all.
Without this patch and previous one, it may take more 20+ seconds for
virtio-scsi to complete disk probe. With the two patches, the time becomes
less than 100ms.
Fixes: c2856ae2f315d75 ("blk-mq: quiesce queue before freeing queue")
Reported-by: Andrew Jones <drjones@redhat.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: linux-scsi@vger.kernel.org
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Tested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-core.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/block/blk-core.c b/block/blk-core.c index f84a9b7b6f5a..947e7a4abd8c 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -762,9 +762,13 @@ void blk_cleanup_queue(struct request_queue *q) * make sure all in-progress dispatch are completed because * blk_freeze_queue() can only complete all requests, and * dispatch may still be in-progress since we dispatch requests - * from more than one contexts + * from more than one contexts. + * + * No need to quiesce queue if it isn't initialized yet since + * blk_freeze_queue() should be enough for cases of passthrough + * request. */ - if (q->mq_ops) + if (q->mq_ops && blk_queue_init_done(q)) blk_mq_quiesce_queue(q); /* for synchronous bio-based driver finish in-flight integrity i/o */ |