Bijan Mottahedeh <bijan.mottahedeh@xxxxxxxxxx> writes:
> Mark a REQ_NOWAIT request for a non-mq queue as unspported instead of
> retryable since otherwise the io_uring layer will keep resubmitting
> the request.
Getting back to this...
Jens, right now (using your io_uring-5.7 or linus' tree) fio's
t/io_uring will never get io completions when run against a file on a
file system that is backed by lvm. The system will have one workqueue
per sqe submitted, all spinning, eating up CPU time.
# ./t/io_uring /mnt/test/poo
Added file /mnt/test/poo
sq_ring ptr = 0x0x7fbed40ae000
sqes ptr = 0x0x7fbed40ac000
cq_ring ptr = 0x0x7fbed40aa000
polled=1, fixedbufs=1, buffered=0 QD=128, sq_ring=128, cq_ring=256
submitter=3851
IOPS=128, IOS/call=6/0, inflight=128 (128)
IOPS=0, IOS/call=0/0, inflight=128 (128)
IOPS=0, IOS/call=0/0, inflight=128 (128)
IOPS=0, IOS/call=0/0, inflight=128 (128)
IOPS=0, IOS/call=0/0, inflight=128 (128)
IOPS=0, IOS/call=0/0, inflight=128 (128)
...
# ps auxw | grep io_wqe
root 3849 80.1 0.0 0 0 ? R 14:32 0:40 [io_wqe_worker-0]
root 3850 0.0 0.0 0 0 ? S 14:32 0:00 [io_wqe_worker-0]
root 3853 72.8 0.0 0 0 ? R 14:32 0:36 [io_wqe_worker-0]
root 3854 81.4 0.0 0 0 ? R 14:32 0:40 [io_wqe_worker-1]
root 3855 74.8 0.0 0 0 ? R 14:32 0:37 [io_wqe_worker-0]
root 3856 74.8 0.0 0 0 ? R 14:32 0:37 [io_wqe_worker-1]
...
# ps auxw | grep io_wqe | grep -v grep | wc -l
129
With this patch applied, the test program will exit without doing I/O
(which I don't think is the right behavior either, right?):
# t/io_uring /mnt/test/poo
Added file /mnt/test/poo
sq_ring ptr = 0x0x7fdb98f00000
sqes ptr = 0x0x7fdb98efe000
cq_ring ptr = 0x0x7fdb98efc000
polled=1, fixedbufs=1, buffered=0 QD=128, sq_ring=128, cq_ring=256
submitter=33233
io: unexpected ret=-95
Your filesystem/driver/kernel doesn't support polled IO
IOPS=128, IOS/call=32/0, inflight=128 (127)
/mnt/test is an xfs file system on top of a linear LVM volume on an nvme
device (with 8 poll queues configured).
-Jeff
>
> Signed-off-by: Bijan Mottahedeh <bijan.mottahedeh@xxxxxxxxxx>
> ---
> block/blk-core.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 5847993..3807140 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -962,14 +962,10 @@ static inline blk_status_t blk_check_zone_append(struct request_queue *q,
> }
>
> /*
> - * Non-mq queues do not honor REQ_NOWAIT, so complete a bio
> - * with BLK_STS_AGAIN status in order to catch -EAGAIN and
> - * to give a chance to the caller to repeat request gracefully.
> + * Non-mq queues do not honor REQ_NOWAIT, return -EOPNOTSUPP.
> */
> - if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q)) {
> - status = BLK_STS_AGAIN;
> - goto end_io;
> - }
> + if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q))
> + goto not_supported;
>
> if (should_fail_bio(bio))
> goto end_io;
