From f51d46d0e7cb5b8494aa534d276a9d8915a2443d Mon Sep 17 00:00:00 2001 From: Vishal Verma Date: Tue, 21 Dec 2021 20:06:19 +0000 Subject: [PATCH] md: add support for REQ_NOWAIT commit 021a24460dc2 ("block: add QUEUE_FLAG_NOWAIT") added support for checking whether a given bdev supports handling of REQ_NOWAIT or not. Since then commit 6abc49468eea ("dm: add support for REQ_NOWAIT and enable it for linear target") added support for REQ_NOWAIT for dm. This uses a similar approach to incorporate REQ_NOWAIT for md based bios. This patch was tested using t/io_uring tool within FIO. A nvme drive was partitioned into 2 partitions and a simple raid 0 configuration /dev/md0 was created. md0 : active raid0 nvme4n1p1[1] nvme4n1p2[0] 937423872 blocks super 1.2 512k chunks Before patch: $ ./t/io_uring /dev/md0 -p 0 -a 0 -d 1 -r 100 Running top while the above runs: $ ps -eL | grep $(pidof io_uring) 38396 38396 pts/2 00:00:00 io_uring 38396 38397 pts/2 00:00:15 io_uring 38396 38398 pts/2 00:00:13 iou-wrk-38397 We can see iou-wrk-38397 io worker thread created which gets created when io_uring sees that the underlying device (/dev/md0 in this case) doesn't support nowait. After patch: $ ./t/io_uring /dev/md0 -p 0 -a 0 -d 1 -r 100 Running top while the above runs: $ ps -eL | grep $(pidof io_uring) 38341 38341 pts/2 00:10:22 io_uring 38341 38342 pts/2 00:10:37 io_uring After running this patch, we don't see any io worker thread being created which indicated that io_uring saw that the underlying device does support nowait. This is the exact behaviour noticed on a dm device which also supports nowait. For all the other raid personalities except raid0, we would need to train pieces which involves make_request fn in order for them to correctly handle REQ_NOWAIT. Reviewed-by: Jens Axboe Signed-off-by: Vishal Verma Signed-off-by: Song Liu --- drivers/md/md.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/drivers/md/md.c b/drivers/md/md.c index 7fbf6f0ac01b..c6de7d4bfe4d 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -418,6 +418,12 @@ check_suspended: rcu_read_lock(); if (is_suspended(mddev, bio)) { DEFINE_WAIT(__wait); + /* Bail out if REQ_NOWAIT is set for the bio */ + if (bio->bi_opf & REQ_NOWAIT) { + rcu_read_unlock(); + bio_wouldblock_error(bio); + return; + } for (;;) { prepare_to_wait(&mddev->sb_wait, &__wait, TASK_UNINTERRUPTIBLE); @@ -5787,6 +5793,7 @@ int md_run(struct mddev *mddev) int err; struct md_rdev *rdev; struct md_personality *pers; + bool nowait = true; if (list_empty(&mddev->disks)) /* cannot run an array with no devices.. */ @@ -5857,8 +5864,13 @@ int md_run(struct mddev *mddev) } } sysfs_notify_dirent_safe(rdev->sysfs_state); + nowait = nowait && blk_queue_nowait(bdev_get_queue(rdev->bdev)); } + /* Set the NOWAIT flags if all underlying devices support it */ + if (nowait) + blk_queue_flag_set(QUEUE_FLAG_NOWAIT, mddev->queue); + if (!bioset_initialized(&mddev->bio_set)) { err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS); if (err) @@ -7003,6 +7015,15 @@ static int hot_add_disk(struct mddev *mddev, dev_t dev) if (!mddev->thread) md_update_sb(mddev, 1); /* + * If the new disk does not support REQ_NOWAIT, + * disable on the whole MD. + */ + if (!blk_queue_nowait(bdev_get_queue(rdev->bdev))) { + pr_info("%s: Disabling nowait because %s does not support nowait\n", + mdname(mddev), bdevname(rdev->bdev, b)); + blk_queue_flag_clear(QUEUE_FLAG_NOWAIT, mddev->queue); + } + /* * Kick recovery, maybe this spare has to be added to the * array immediately. */ -- 2.11.0