lkml.org 
[lkml]   [2018]   [Sep]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH AUTOSEL 4.18 88/92] blk-mq: avoid to synchronize rcu inside blk_cleanup_queue()
    Date
    From: Ming Lei <ming.lei@redhat.com>

    [ Upstream commit 1311326cf4755c7ffefd20f576144ecf46d9906b ]

    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>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    block/blk-core.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/block/blk-core.c b/block/blk-core.c
    index 1646ea85dade..0f5b314fc810 100644
    --- a/block/blk-core.c
    +++ b/block/blk-core.c
    @@ -791,9 +791,13 @@ 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 */
    --
    2.17.1
    \
     
     \ /
      Last update: 2018-09-15 03:47    [W:4.146 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site