Re: [RFC PATCH 1/1] drivers/vhost: vhost-blk accelerator for virtio-blk guests

["Denis V. Lunev via Virtualization" <virtualization@lists.linux-foundation.org>]

On 26.07.2022 16:45, Michael S. Tsirkin wrote:
> On Mon, Jul 25, 2022 at 11:27:53PM +0300, Andrey Zhadchenko wrote:
>> Although QEMU virtio is quite fast, there is still some room for
>> improvements. Disk latency can be reduced if we handle virito-blk requests
>> in host kernel istead of passing them to QEMU. The patch adds vhost-blk
>> kernel module to do so.
>>
>> Some test setups:
>> fio --direct=1 --rw=randread  --bs=4k  --ioengine=libaio --iodepth=128
>> QEMU drive options: cache=none
>> filesystem: xfs
>>
>> SSD:
>>                 | randread, IOPS  | randwrite, IOPS |
>> Host           |      95.8k      |      85.3k      |
>> QEMU virtio    |      57.5k      |      79.4k      |
>> QEMU vhost-blk |      95.6k      |      84.3k      |
>>
>> RAMDISK (vq == vcpu):
>>                   | randread, IOPS | randwrite, IOPS |
>> virtio, 1vcpu    |      123k      |      129k       |
>> virtio, 2vcpu    |      253k (??) |      250k (??)  |
>> virtio, 4vcpu    |      158k      |      154k       |
>> vhost-blk, 1vcpu |      110k      |      113k       |
>> vhost-blk, 2vcpu |      247k      |      252k       |
>> vhost-blk, 4vcpu |      576k      |      567k       |
>>
>> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
>
> Sounds good to me. What this depends on is whether some userspace
> will actually use it. In the past QEMU rejected support for vhost-blk,
> if this time it fares better then I won't have a problem merging
> the kernel bits.

In general, we are going to use this in production for our
next generation product and thus we would be very glad
to see both parts, i.e. in-kernel and in-QEMU to be merged
to reduce our support costs.

I think that numbers are talking on themselves and this
would be quite beneficial for all parties especially keeping
in mind that QCOW2 is also now supported for this kind
of IO engine.

Den
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