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.
Signed-off-by: Vishal Verma <vverma@xxxxxxxxxxxxxxxx>
---
drivers/md/md.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5111ed966947..73089776475f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5792,6 +5792,7 @@ 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.. */
@@ -5862,8 +5863,13 @@ 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)
@@ -7007,6 +7013,14 @@ static int hot_add_disk(struct mddev *mddev, dev_t dev)
set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
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.
--
2.17.1
