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[Qemu-devel] Re: [RFC] vhost-blk implementation

From: Michael S. Tsirkin
Subject: [Qemu-devel] Re: [RFC] vhost-blk implementation
Date: Tue, 23 Mar 2010 14:39:16 +0200
User-agent: Mutt/1.5.19 (2009-01-05)

On Mon, Mar 22, 2010 at 05:34:04PM -0700, Badari Pulavarty wrote:
> Write Results:
> ==============
> I see degraded IO performance when doing sequential IO write
> tests with vhost-blk compared to virtio-blk.
> # time dd of=/dev/vda if=/dev/zero bs=2M oflag=direct
> I get ~110MB/sec with virtio-blk, but I get only ~60MB/sec with
> vhost-blk. Wondering why ?

Try to look and number of interrupts and/or number of exits.

It could also be that you are overrunning some queue.

I don't see any exit mitigation strategy in your patch:
when there are already lots of requests in a queue, it's usually
a good idea to disable notifications and poll the
queue as requests complete. That could help performance.


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