Re: [RFC patch 0/1] block: vhost-blk backend

[Stefan Hajnoczi]

On Wed, Oct 05, 2022 at 12:14:18PM +0300, Andrey Zhadchenko wrote:
> On 10/4/22 21:13, Stefan Hajnoczi wrote:
> > On Mon, Jul 25, 2022 at 11:55:26PM +0300, Andrey Zhadchenko wrote:
> > > Although QEMU virtio-blk is quite fast, there is still some room for
> > > improvements. Disk latency can be reduced if we handle virito-blk requests
> > > in host kernel so we avoid a lot of syscalls and context switches.
> > > 
> > > The biggest disadvantage of this vhost-blk flavor is raw format.
> > > Luckily Kirill Thai proposed device mapper driver for QCOW2 format to 
> > > attach
> > > files as block devices: 
> > > https://www.spinics.net/lists/kernel/msg4292965.html
> > > 
> > > Also by using kernel modules we can bypass iothread limitation and finaly 
> > > scale
> > > block requests with cpus for high-performance devices. This is planned to 
> > > be
> > > implemented in next version.
> > 
> > Hi Andrey,
> > Do you have a new version of this patch series that uses multiple
> > threads?
> > 
> > I have been playing with vq-IOThread mapping in QEMU and would like to
> > benchmark vhost-blk vs QEMU virtio-blk mq IOThreads:
> > https://gitlab.com/stefanha/qemu/-/tree/virtio-blk-mq-iothread-prototype
> > 
> > Thanks,
> > Stefan
> 
> Hi Stefan
> For now my multi-threaded version is only available for Red Hat 9 5.14.0
> kernel. If you really want you can grab it from here:
> https://lists.openvz.org/pipermail/devel/2022-September/079951.html (kernel)
> For QEMU part all you need is adding to vhost_blk_start something like:
> 
> #define VHOST_SET_NWORKERS _IOW(VHOST_VIRTIO, 0x1F, int)
> ioctl(s->vhostfd, VHOST_SET_NWORKERS, &nworkers);
> 
> Or you can wait a bit. I should be able to send second versions by the end
> of the week (Monday in worst case).

Thanks, I will wait for the next revision.

Stefan

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