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authorMing Lei <ming.lei@redhat.com>2018-06-25 19:31:49 +0800
committerJens Axboe <axboe@kernel.dk>2018-07-09 09:07:52 -0600
commit1311326cf4755c7ffefd20f576144ecf46d9906b (patch)
tree9f973618b2b1d61520c37a16dbb1d27399f48632 /block/blk-core.c
parent97889f9ac24f8d2fc8e703ea7f80c162bab10d4d (diff)
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/blk-core.c')
-rw-r--r--block/blk-core.c8
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 */