This is a note to let you know that I've just added the patch titled block: avoid to quiesce queue in elevator_init_mq to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: block-avoid-to-quiesce-queue-in-elevator_init_mq.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 245a489e81e13dd55ae46d27becf6d5901eb7828 Mon Sep 17 00:00:00 2001 From: Ming Lei <ming.lei@xxxxxxxxxx> Date: Wed, 17 Nov 2021 19:55:02 +0800 Subject: block: avoid to quiesce queue in elevator_init_mq From: Ming Lei <ming.lei@xxxxxxxxxx> commit 245a489e81e13dd55ae46d27becf6d5901eb7828 upstream. elevator_init_mq() is only called before adding disk, when there isn't any FS I/O, only passthrough requests can be queued, so freezing queue plus canceling dispatch work is enough to drain any dispatch activities, then we can avoid synchronize_srcu() in blk_mq_quiesce_queue(). Long boot latency issue can be fixed in case of lots of disks added during booting. Fixes: 737eb78e82d5 ("block: Delay default elevator initialization") Reported-by: yangerkun <yangerkun@xxxxxxxxxx> Cc: Damien Le Moal <damien.lemoal@xxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> Link: https://lore.kernel.org/r/20211117115502.1600950-1-ming.lei@xxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/elevator.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) --- a/block/elevator.c +++ b/block/elevator.c @@ -694,12 +694,18 @@ void elevator_init_mq(struct request_que if (!e) return; + /* + * We are called before adding disk, when there isn't any FS I/O, + * so freezing queue plus canceling dispatch work is enough to + * drain any dispatch activities originated from passthrough + * requests, then no need to quiesce queue which may add long boot + * latency, especially when lots of disks are involved. + */ blk_mq_freeze_queue(q); - blk_mq_quiesce_queue(q); + blk_mq_cancel_work_sync(q); err = blk_mq_init_sched(q, e); - blk_mq_unquiesce_queue(q); blk_mq_unfreeze_queue(q); if (err) { Patches currently in stable-queue which might be from ming.lei@xxxxxxxxxx are queue-5.15/block-avoid-to-quiesce-queue-in-elevator_init_mq.patch queue-5.15/blk-mq-cancel-blk-mq-dispatch-work-in-both-blk_cleanup_queue-and-disk_release.patch