Re: [PATCH 0/5] Add vhost-blk support

From: Asias He
Date: Wed Jul 18 2012 - 04:11:11 EST

On 07/17/2012 07:11 PM, Stefan Hajnoczi wrote:
On Tue, Jul 17, 2012 at 10:21 AM, Asias He <asias@xxxxxxxxxx> wrote:
On 07/17/2012 04:52 PM, Paolo Bonzini wrote:

Il 17/07/2012 10:29, Asias He ha scritto:

So, vhost-blk at least saves ~6 syscalls for us in each request.

Are they really 6? If I/O is coalesced by a factor of 3, for example
(i.e. each exit processes 3 requests), it's really 2 syscalls per request.

Well. I am counting the number of syscalls in one notify and response
process. Sure the IO can be coalesced.

Linux AIO also supports batching in io_submit() and io_getevents().
Depending on the request pattern in the vring when you process it, you
should be able to do better than 1 set of syscalls per host I/O

Are you taking advantage of that at the moment in your userspace benchmark?

OK. I know that batching in io_submit() and io_getevetns(). There was a patch for kvm tool long time ago. Now, both vhost-blk and kvm tool are not taking advantage of that atm. There are issues: e.g. How many number of request we want to batch? Does this batching hurt latency?


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