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

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Date:   Mon, 5 Nov 2018 11:00:23 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Vitaly Mayatskikh <v.mayatskih@...il.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH 0/1] vhost: add vhost_blk driver


On 2018/11/3 上午2:21, Vitaly Mayatskikh wrote:
> vhost_blk is a host-side kernel mode accelerator for virtio-blk. The
> driver allows VM to reach a near bare-metal disk performance. See IOPS
> numbers below (fio --rw=randread --bs=4k).
>
> This implementation uses kiocb interface. It is slightly slower than
> going directly through bio, but is simpler and also works with disk
> images placed on a file system.
>
> # 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
>
> 1  171k  151k  148k 151k 195k  187k  175k
> 2  328k  302k  249k 241k 349k  334k  296k
> 3  479k  437k  179k 174k 501k  464k  404k
> 4  622k  568k  143k 183k 620k  580k  492k
> 5  755k  697k  136k 128k 737k  693k  579k
> 6  887k  808k  131k 120k 830k  782k  640k
> 7  1004k 926k  126k 131k 926k  863k  693k
> 8  1099k 1015k 117k 115k 1001k 931k  712k
> 9  1194k 1119k 115k 111k 1055k 991k  711k
> 10 1278k 1207k 109k 114k 1130k 1046k 695k
> 11 1345k 1280k 110k 108k 1119k 1091k 663k
> 12 1411k 1356k 104k 106k 1201k 1142k 629k
> 13 1466k 1423k 106k 106k 1260k 1170k 607k
> 14 1517k 1486k 103k 106k 1296k 1179k 589k
> 15 1552k 1543k 102k 102k 1322k 1191k 571k
> 16 1480k 1506k 101k 102k 1346k 1202k 566k
>
> Vitaly Mayatskikh (1):
>    Add vhost_blk driver
>
>   drivers/vhost/Kconfig  |  13 ++
>   drivers/vhost/Makefile |   3 +
>   drivers/vhost/blk.c    | 510 +++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 526 insertions(+)
>   create mode 100644 drivers/vhost/blk.c
>

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?

Thanks