linux-kernel - Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device

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Date:	Mon, 01 Aug 2011 13:46:33 +0800
From:	Liu Yuan <namei.unix@...il.com>
To:	Badari Pulavarty <pbadari@...ibm.com>
CC:	Stefan Hajnoczi <stefanha@...il.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Khoa Huynh <khoa@...ibm.com>
Subject: Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block
 device

On 07/30/2011 02:12 AM, Badari Pulavarty wrote:
> Hi Liu Yuan,
>
> I am glad to see that you started looking at vhost-blk.   I did an 
> attempt year ago to improve block
> performance using vhost-blk approach.
>
> http://lwn.net/Articles/379864/
> http://lwn.net/Articles/382543/
>
> I will take a closer look at your patchset to find differences and 
> similarities.
>
> - I focused on using vfs interfaces in the kernel, so that I can use 
> it for file-backed devices.
> Our use-case scenario is mostly file-backed images.
>
vhost-blk's that uses Linux AIO also support file-backed images. 
Actually, I have run Guests both on raw partition and raw file images.

> - In few cases, virtio-blk did outperform vhost-blk -- which was 
> counter intuitive - but
> couldn't exactly nail down. why ?
>
> - I had to implement my own threads for parellism. I see that you are 
> using aio infrastructure
> to get around it.
>
> - In our high scale performance testing, what we found is block-backed 
> device performance is
> pretty close to bare-metal (91% of bare-metal). vhost-blk didn't add 
> any major benefits to it.
> I am curious on your performance analysis & data on where you see the 
> gains and why ?
>
Possibly bypass vfs-layer and translate sg lists from virtio buffer into 
BIOs would benefit the block-backed device. I'll give it a try later.

> Hence I prioritized my work low :(
>
> Now that you are interested in driving this, I am happy to work with 
> you and see what
> vhost-blk brings to the tables. (even if helps us improve virtio-blk).
>
> Thanks,
> Badari
>
>

That's great.

Yuan
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