Re: ublk-qcow2: ublk-qcow2 is available

Ziyang Zhang
2022-10-08T08:43:59Z

On 2022/10/5 12:18, Ming Lei wrote:
> On Tue, Oct 04, 2022 at 09:53:32AM -0400, Stefan Hajnoczi wrote:
>> On Tue, 4 Oct 2022 at 05:44, Ming Lei <tom.leiming@gmail.com> wrote:
>>>
>>> On Mon, Oct 03, 2022 at 03:53:41PM -0400, Stefan Hajnoczi wrote:
>>>> On Fri, Sep 30, 2022 at 05:24:11PM +0800, Ming Lei wrote:
>>>>> ublk-qcow2 is available now.
>>>>
>>>> Cool, thanks for sharing!
>>>>
>>>>>
>>>>> So far it provides basic read/write function, and compression and snapshot
>>>>> aren't supported yet. The target/backend implementation is completely
>>>>> based on io_uring, and share the same io_uring with ublk IO command
>>>>> handler, just like what ublk-loop does.
>>>>>
>>>>> Follows the main motivations of ublk-qcow2:
>>>>>
>>>>> - building one complicated target from scratch helps libublksrv APIs/functions
>>>>> become mature/stable more quickly, since qcow2 is complicated and needs more
>>>>> requirement from libublksrv compared with other simple ones(loop, null)
>>>>>
>>>>> - there are several attempts of implementing qcow2 driver in kernel, such as
>>>>> ``qloop`` [2], ``dm-qcow2`` [3] and ``in kernel qcow2(ro)`` [4], so ublk-qcow2
>>>>> might useful be for covering requirement in this field
>>>>>
>>>>> - performance comparison with qemu-nbd, and it was my 1st thought to evaluate
>>>>> performance of ublk/io_uring backend by writing one ublk-qcow2 since ublksrv
>>>>> is started
>>>>>
>>>>> - help to abstract common building block or design pattern for writing new ublk
>>>>> target/backend
>>>>>
>>>>> So far it basically passes xfstest(XFS) test by using ublk-qcow2 block
>>>>> device as TEST_DEV, and kernel building workload is verified too. Also
>>>>> soft update approach is applied in meta flushing, and meta data
>>>>> integrity is guaranteed, 'make test T=qcow2/040' covers this kind of
>>>>> test, and only cluster leak is reported during this test.
>>>>>
>>>>> The performance data looks much better compared with qemu-nbd, see
>>>>> details in commit log[1], README[5] and STATUS[6]. And the test covers both
>>>>> empty image and pre-allocated image, for example of pre-allocated qcow2
>>>>> image(8GB):
>>>>>
>>>>> - qemu-nbd (make test T=qcow2/002)
>>>>
>>>> Single queue?
>>>
>>> Yeah.
>>>
>>>>
>>>>> randwrite(4k): jobs 1, iops 24605
>>>>> randread(4k): jobs 1, iops 30938
>>>>> randrw(4k): jobs 1, iops read 13981 write 14001
>>>>> rw(512k): jobs 1, iops read 724 write 728
>>>>
>>>> Please try qemu-storage-daemon's VDUSE export type as well. The
>>>> command-line should be similar to this:
>>>>
>>>> # modprobe virtio_vdpa # attaches vDPA devices to host kernel
>>>
>>> Not found virtio_vdpa module even though I enabled all the following
>>> options:
>>>
>>> --- vDPA drivers
>>> <M> vDPA device simulator core
>>> <M> vDPA simulator for networking device
>>> <M> vDPA simulator for block device
>>> <M> VDUSE (vDPA Device in Userspace) support
>>> <M> Intel IFC VF vDPA driver
>>> <M> Virtio PCI bridge vDPA driver
>>> <M> vDPA driver for Alibaba ENI
>>>
>>> BTW, my test environment is VM and the shared data is done in VM too, and
>>> can virtio_vdpa be used inside VM?
>>
>> I hope Xie Yongji can help explain how to benchmark VDUSE.
>>
>> virtio_vdpa is available inside guests too. Please check that
>> VIRTIO_VDPA ("vDPA driver for virtio devices") is enabled in "Virtio
>> drivers" menu.
>>
>>>
>>>> # modprobe vduse
>>>> # qemu-storage-daemon \
>>>> --blockdev file,filename=test.qcow2,cache.direct=of|off,aio=native,node-name=file \
>>>> --blockdev qcow2,file=file,node-name=qcow2 \
>>>> --object iothread,id=iothread0 \
>>>> --export vduse-blk,id=vduse0,name=vduse0,num-queues=$(nproc),node-name=qcow2,writable=on,iothread=iothread0
>>>> # vdpa dev add name vduse0 mgmtdev vduse
>>>>
>>>> A virtio-blk device should appear and xfstests can be run on it
>>>> (typically /dev/vda unless you already have other virtio-blk devices).
>>>>
>>>> Afterwards you can destroy the device using:
>>>>
>>>> # vdpa dev del vduse0
>>>>
>>>>>
>>>>> - ublk-qcow2 (make test T=qcow2/022)
>>>>
>>>> There are a lot of other factors not directly related to NBD vs ublk. In
>>>> order to get an apples-to-apples comparison with qemu-* a ublk export
>>>> type is needed in qemu-storage-daemon. That way only the difference is
>>>> the ublk interface and the rest of the code path is identical, making it
>>>> possible to compare NBD, VDUSE, ublk, etc more precisely.
>>>
>>> Maybe not true.
>>>
>>> ublk-qcow2 uses io_uring to handle all backend IO(include meta IO) completely,
>>> and so far single io_uring/pthread is for handling all qcow2 IOs and IO
>>> command.
>>
>> qemu-nbd doesn't use io_uring to handle the backend IO, so we don't
>
> I tried to use it via --aio=io_uring for setting up qemu-nbd, but not succeed.
>
>> know whether the benchmark demonstrates that ublk is faster than NBD,
>> that the ublk-qcow2 implementation is faster than qemu-nbd's qcow2,
>> whether there are miscellaneous implementation differences between
>> ublk-qcow2 and qemu-nbd (like using the same io_uring context for both
>> ublk and backend IO), or something else.
>
> The theory shouldn't be too complicated:
>
> 1) io uring passthough(pt) communication is fast than socket, and io command
> is carried over io_uring pt commands, and should be fast than virio
> communication too.
>
> 2) io uring io handling is fast than libaio which is taken in the
> test on qemu-nbd, and all qcow2 backend io(include meta io) is handled
> by io_uring.
>
> https://github.com/ming1/ubdsrv/blob/master/tests/common/qcow2_common
>
> 3) ublk uses one single io_uring to handle all io commands and qcow2
> backend IOs, so batching handling is common, and it is easy to see
> dozens of IOs/io commands handled in single syscall, or even more.
>
>>
>> I'm suggesting measuring changes to just 1 variable at a time.
>> Otherwise it's hard to reach a conclusion about the root cause of the
>> performance difference. Let's learn why ublk-qcow2 performs well.
>
> Turns out the latest Fedora 37-beta doesn't support vdpa yet, so I built
> qemu from the latest github tree, and finally it starts to work. And test kernel
> is v6.0 release.
>
> Follows the test result, and all three devices are setup as single
> queue, and all tests are run in single job, still done in one VM, and
> the test images are stored on XFS/virito-scsi backed SSD.
>
> The 1st group tests all three block device which is backed by empty
> qcow2 image.
>
> The 2nd group tests all the three block devices backed by pre-allocated
> qcow2 image.
>
> Except for big sequential IO(512K), there is still not small gap between
> vdpa-virtio-blk and ublk.
>
> 1. run fio on block device over empty qcow2 image
> 1) qemu-nbd
> running qcow2/001
> run perf test on empty qcow2 image via nbd
> fio (nbd(/mnt/data/ublk_null_8G_nYbgF.qcow2), libaio, bs 4k, dio, hw queues:1)...
> randwrite: jobs 1, iops 8549
> randread: jobs 1, iops 34829
> randrw: jobs 1, iops read 11363 write 11333
> rw(512k): jobs 1, iops read 590 write 597
>
>
> 2) ublk-qcow2
> running qcow2/021
> run perf test on empty qcow2 image via ublk
> fio (ublk/qcow2( -f /mnt/data/ublk_null_8G_s761j.qcow2), libaio, bs 4k, dio, hw queues:1, uring_comp: 0, get_data: 0).
> randwrite: jobs 1, iops 16086
> randread: jobs 1, iops 172720
> randrw: jobs 1, iops read 35760 write 35702
> rw(512k): jobs 1, iops read 1140 write 1149
>
> 3) vdpa-virtio-blk
> running debug/test_dev
> run io test on specified device
> fio (vdpa(/dev/vdc), libaio, bs 4k, dio, hw queues:1)...
> randwrite: jobs 1, iops 8626
> randread: jobs 1, iops 126118
> randrw: jobs 1, iops read 17698 write 17665
> rw(512k): jobs 1, iops read 1023 write 1031
>
>
> 2. run fio on block device over pre-allocated qcow2 image
> 1) qemu-nbd
> running qcow2/002
> run perf test on pre-allocated qcow2 image via nbd
> fio (nbd(/mnt/data/ublk_data_8G_sc0SB.qcow2), libaio, bs 4k, dio, hw queues:1)...
> randwrite: jobs 1, iops 21439
> randread: jobs 1, iops 30336
> randrw: jobs 1, iops read 11476 write 11449
> rw(512k): jobs 1, iops read 718 write 722
>
> 2) ublk-qcow2
> running qcow2/022
> run perf test on pre-allocated qcow2 image via ublk
> fio (ublk/qcow2( -f /mnt/data/ublk_data_8G_yZiaJ.qcow2), libaio, bs 4k, dio, hw queues:1, uring_comp: 0, get_data: 0).
> randwrite: jobs 1, iops 98757
> randread: jobs 1, iops 110246
> randrw: jobs 1, iops read 47229 write 47161
> rw(512k): jobs 1, iops read 1416 write 1427
>
> 3) vdpa-virtio-blk
> running debug/test_dev
> run io test on specified device
> fio (vdpa(/dev/vdc), libaio, bs 4k, dio, hw queues:1)...
> randwrite: jobs 1, iops 47317
> randread: jobs 1, iops 74092
> randrw: jobs 1, iops read 27196 write 27234
> rw(512k): jobs 1, iops read 1447 write 1458
>
>

Hi All,

We are interested in VDUSE vs UBLK, too. And I have tested them with nullblk backend.
Let me share some results here.

I setup UBLK with:
ublk add -t loop -f /dev/nullb0 -d QUEUE_DEPTH -q NR_QUEUE

I setup VDUSE with:
qemu-storage-daemon \
--chardev socket,id=charmonitor,path=/tmp/qmp.sock,server=on,wait=off \
--monitor chardev=charmonitor \
--blockdev driver=host_device,cache.direct=on,filename=/dev/nullb0,node-name=disk0 \
--export vduse-blk,id=test,node-name=disk0,name=vduse_test,writable=on,num-queues=NR_QUEUE,queue-size=QUEUE_DEPTH

Here QUEUE_DEPTH is 1, 32 or 128 and NR_QUEUE is 1 or 4.

Note:
(1) VDUSE requires QUEUE_DEPTH >= 2. I cannot setup QUEUE_DEPTH to 1.
(2) I use qemu 7.1.0-rc3. It supports vduse-blk.
(3) I do not use ublk null target so that the test is fair.
(4) I setup fio with direct=1, bs=4k.

------------------------------
1 job 1 iodepth, lat（usec)
vduse ublk
seq-read 22.55 11.15
rand-read 22.49 11.17
seq-write 25.67 10.25
rand-write 24.13 10.16

------------------------------
1 job 32 iodepth, iops（k)
vduse ublk
seq-read 166 207
rand-read 150 204
seq-write 131 359
rand-write 129 363

------------------------------
4job 128 iodepth, iops (k)

vduse ublk
seq-read 318 984
rand-read 307 929
seq-write 221 924
rand-write 217 917

Regards,
Zhang