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

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Date:	Fri, 29 Jul 2011 11:12:02 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Liu Yuan <namei.unix@...il.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

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.

- 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 ?

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


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