On 1/1/22 5:11 PM, Song Liu wrote:
On Wed, Dec 22, 2021 at 6:57 PM Song Liu <song@xxxxxxxxxx> wrote:
On Tue, Dec 21, 2021 at 12:06 PM Vishal Verma <vverma@xxxxxxxxxxxxxxxx> wrote:
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>
I have made some changes and applied the set to md-next. However,
I think we don't yet have enough test coverage. Please continue testing
the code and send fixes on top of it. Based on the test results, we will
see whether we can ship it in the next merge window.
Note, md-next branch doesn't have [1], so we need to cherry-pick it
for testing.
I went through all these changes again and tested many (but not all)
cases. The latest version is available in md-next branch.
Vishal, please run tests on this version and send fixes if anything
is broken.
Thanks,
Song
Thanks Song. This latest version looks good!
And yes, will report out if I notice any issues or anything.
