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Lunev" , Stefano Garzarella Subject: Re: ublk-qcow2: ublk-qcow2 is available Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, Oct 07, 2022 at 07:21:51PM +0800, Yongji Xie wrote: > On Fri, Oct 7, 2022 at 6:51 PM Ming Lei wrote: > > > > On Fri, Oct 07, 2022 at 06:04:29PM +0800, Yongji Xie wrote: > > > On Thu, Oct 6, 2022 at 7:24 PM Ming Lei wrote: > > > > > > > > On Wed, Oct 05, 2022 at 08:21:45AM -0400, Stefan Hajnoczi wrote: > > > > > On Wed, 5 Oct 2022 at 00:19, 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 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 > > > > > > > > vDPA device simulator core > > > > > > > > vDPA simulator for networking device > > > > > > > > vDPA simulator for block device > > > > > > > > VDUSE (vDPA Device in Userspace) support > > > > > > > > Intel IFC VF vDPA driver > > > > > > > > Virtio PCI bridge vDPA driver > > > > > > > > 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 agree with the theory but theory has to be tested through > > > > > experiments in order to validate it. We can all learn from systematic > > > > > performance analysis - there might even be bottlenecks in ublk that > > > > > can be solved to improve performance further. > > > > > > > > Indeed, one thing is that ublk uses get user pages to retrieve user pages > > > > for copying data, this way may add latency for big chunk IO, since > > > > latency of get user pages should be increased linearly by nr_pages. > > > > > > > > I looked into vduse code a bit too, and vduse still needs the page copy, > > > > but lots of bounce pages are allocated and cached in the whole device > > > > lifetime, this way can void the latency for retrieving & allocating > > > > pages runtime with cost of extra memory consumption. Correct me > > > > if it is wrong, Xie Yongji or anyone? > > > > > > > > > > Yes, you are right. Another way is registering the preallocated > > > userspace memory as bounce buffer. > > > > Thanks for the clarification. > > > > IMO, the pages consumption is too much for vduse, each vdpa device > > has one vduse_iova_domain which may allocate 64K bounce pages at most, > > and these pages won't be freed until freeing the device. > > > > Yes, actually in our initial design, this can be mitigated by some > memory reclaim mechanism and zero copy support. Even we can let > multiple vdpa device share one iova domain. I think zero copy is great, especially for big chunk IO request. Thanks, Ming