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Date: Wed, 20 Mar 2013 09:11:30 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130320081130.GA5953@stefanha-thinkpad.muc.redhat.com>
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Subject: Re: [Qemu-devel] kvm suspend performance
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To: Thomas Knauth <thomas.knauth@gmx.de>
Cc: qemu-devel@nongnu.org

On Tue, Mar 19, 2013 at 05:24:59PM +0100, Thomas Knauth wrote:
> lately I've been playing around with qemu's/kvm's suspend (to disk) and
> resume. My initial expectation was that both operations are I/O bound. So
> it surprised me to see that suspend to disk seems to be CPU-bound.
> Suspending a VM with 1.5 GB memory takes 55 seconds. This works out to less
> than 30 MB/s. Again, I was expecting to be I/O bound and reach 100 MB/s
> (and more). I am talking to qemu/kvm via libvirt. Not sure if this matters.
> 
> I am looking for a hint what the issue could be here. Hopefully with
> pointers to the (offending) code.

Hi Thomas,
Please provide more details about the issue:

Which QEMU or libvirt command are you using to suspend the guest to
disk?

Why do you say it is CPU-bound?  Did you use a tool like vmstat or
simply because it does 30 MB/s instead of the expected 100 MB/s?

Which versions of libvirt and QEMU are you using?

Stefan