linux-kernel - Re: [PATCH 0/1] vhost: add vhost

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Date:   Sun, 4 Nov 2018 22:23:04 -0500
From:   Vitaly Mayatskih <v.mayatskih@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, stefanha@...hat.com
Subject: Re: [PATCH 0/1] vhost: add vhost_blk driver

On Sun, Nov 4, 2018 at 10:00 PM Jason Wang <jasowang@...hat.com> wrote:

> > # fio num-jobs
> > # A: bare metal over block
> > # B: bare metal over file
> > # C: virtio-blk over block
> > # D: virtio-blk over file
> > # E: vhost-blk bio over block
> > # F: vhost-blk kiocb over block
> > # G: vhost-blk kiocb over file
> > #
> > #  A     B     C    D    E     F     G

> > 16 1480k 1506k 101k 102k 1346k 1202k 566k

> Hi:
>
> Thanks for the patches.
>
> This is not the first attempt for having vhost-blk:
>
> - Badari's version: https://lwn.net/Articles/379864/
>
> - Asias' version: https://lwn.net/Articles/519880/
>
> It's better to describe the differences (kiocb vs bio? performance?).
> E.g if my memory is correct, Asias said it doesn't give much improvement
> compared with userspace qemu.
>
> And what's more important, I believe we tend to use virtio-scsi nowdays.
> So what's the advantages of vhost-blk over vhost-scsi?

Hi,

Yes, I saw both. Frankly, my implementation is not that different,
because the whole thing has only twice more LOC that vhost/test.c.

I posted my numbers (see in quoted text above the 16 queues case),
IOPS goes from ~100k to 1.2M and almost reaches the physical
limitation of the backend.

submit_bio() is a bit faster, but can't be used for disk images placed
on a file system. I have that submit_bio implementation too.

Storage industry is shifting away from SCSI, which has a scaling
problem. I can compare vhost-scsi vs vhost-blk if you are curious.

Thanks!
-- 
wbr, Vitaly