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From: "Denis V. Lunev" <[email protected]>
To: Stefan Hajnoczi <[email protected]>, Ming Lei <[email protected]>
Cc: [email protected], [email protected],
	[email protected],
	Kirill Tkhai <[email protected]>,
	Manuel Bentele <[email protected]>,
	[email protected], Kevin Wolf <[email protected]>,
	[email protected], Xie Yongji <[email protected]>,
	Stefano Garzarella <[email protected]>
Subject: Re: ublk-qcow2: ublk-qcow2 is available
Date: Tue, 4 Oct 2022 01:57:50 +0200	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <Yzs9xQlVuW41TuNC@fedora>

On 10/3/22 21:53, 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!
yep

>> 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
There is one important thing to keep in mind about all partly-userspace
implementations though:
* any single allocation happened in the context of the
    userspace daemon through try_to_free_pages() in
    kernel has a possibility to trigger the operation,
    which will require userspace daemon action, which
    is inside the kernel now.
* the probability of this is higher in the overcommitted
    environment

This was the main motivation of us in favor for the in-kernel
implementation.

>> - 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?
>
>> 	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
>    # 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
but this would be anyway limited by a single thread doing AIO in
qemu-storage-daemon, I believe.


>> - 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.
>
> I think that comparison is interesting before comparing different qcow2
> implementations because qcow2 sits on top of too much other code. It's
> hard to know what should be accounted to configuration differences,
> implementation differences, or fundamental differences that cannot be
> overcome (this is the interesting part!).
>
>> 	randwrite(4k): jobs 1, iops 104481
>> 	randread(4k): jobs 1, iops 114937
>> 	randrw(4k): jobs 1, iops read 53630 write 53577
>> 	rw(512k): jobs 1, iops read 1412 write 1423
>>
>> Also ublk-qcow2 aligns queue's chunk_sectors limit with qcow2's cluster size,
>> which is 64KB at default, this way simplifies backend io handling, but
>> it could be increased to 512K or more proper size for improving sequential
>> IO perf, just need one coroutine to handle more than one IOs.
>>
>>
>> [1] https://github.com/ming1/ubdsrv/commit/9faabbec3a92ca83ddae92335c66eabbeff654e7
>> [2] https://upcommons.upc.edu/bitstream/handle/2099.1/9619/65757.pdf?sequence=1&isAllowed=y
>> [3] https://lwn.net/Articles/889429/
>> [4] https://lab.ks.uni-freiburg.de/projects/kernel-qcow2/repository
>> [5] https://github.com/ming1/ubdsrv/blob/master/qcow2/README.rst
>> [6] https://github.com/ming1/ubdsrv/blob/master/qcow2/STATUS.rst

interesting...

Den

  reply	other threads:[~2022-10-03 23:58 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-30  9:24 ublk-qcow2: ublk-qcow2 is available Ming Lei
2022-10-03 19:53 ` Stefan Hajnoczi
2022-10-03 23:57   ` Denis V. Lunev [this message]
2022-10-05 15:11     ` Stefan Hajnoczi
2022-10-06 10:26       ` Ming Lei
2022-10-06 13:59         ` Stefan Hajnoczi
2022-10-06 15:09           ` Ming Lei
2022-10-06 18:29             ` Stefan Hajnoczi
2022-10-07 11:21               ` Ming Lei
2022-10-04  9:43   ` Ming Lei
2022-10-04 13:53     ` Stefan Hajnoczi
2022-10-05  4:18       ` Ming Lei
2022-10-05 12:21         ` Stefan Hajnoczi
2022-10-05 12:38           ` Denis V. Lunev
2022-10-06 11:24           ` Ming Lei
2022-10-07 10:04             ` Yongji Xie
2022-10-07 10:51               ` Ming Lei
2022-10-07 11:21                 ` Yongji Xie
2022-10-07 11:23                   ` Ming Lei
2022-10-08  8:43         ` Ziyang Zhang
2022-10-12 14:22           ` Stefan Hajnoczi
2022-10-13  6:48             ` Yongji Xie
2022-10-13 16:02               ` Stefan Hajnoczi
2022-10-14 12:56               ` Ming Lei
2022-10-17 11:11                 ` Yongji Xie
2022-10-18  6:59                   ` Ming Lei
2022-10-18 13:17                     ` Yongji Xie
2022-10-18 14:54                       ` Stefan Hajnoczi
2022-10-19  9:09                         ` Ming Lei
2022-10-24 16:11                           ` Stefan Hajnoczi
2022-10-21  5:33                         ` Yongji Xie
2022-10-21  6:30                           ` Jason Wang
2022-10-25  8:17                             ` Yongji Xie
2022-10-25 12:02                               ` Stefan Hajnoczi
2022-10-28 13:33                                 ` Yongji Xie
2022-11-01  2:36                                 ` Jason Wang
2022-11-02 19:13                                   ` Stefan Hajnoczi
2022-11-04  6:55                                     ` Jason Wang
2022-10-21  6:28                     ` Jason Wang
2022-10-06 10:14       ` Richard W.M. Jones
2022-10-12 14:15         ` Stefan Hajnoczi
2022-10-13  1:50           ` Ming Lei
2022-10-13 16:01             ` Stefan Hajnoczi
2022-10-04  5:43 ` Manuel Bentele

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