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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Tue, 22 May 2012 21:41:41 +1000
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Subject: Re: [Qemu-devel] [PATCH] Add a memory barrier to DMA functions
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>, David Gibson <david@gibson.dropbear.id.au>

On Tue, 2012-05-22 at 14:14 +0300, Michael S. Tsirkin wrote:
> > The baseline is the laptop without kvm talking to the server. The
> > TCP_STREAM test results are:
> 
> It's not a good test. The thing most affecting throughput results is
> how
> much CPU does you guest get. So as a minumum you need to measure CPU
> utilization on the host and divide by that. 

The simple fact that we don't reach the baseline while in qemu seems to
be a reasonably good indication that we tend to be CPU bound already so
it's not -that- relevant. It would be if we were saturating the network.

But yes, I can try to do more tests tomorrow, it would be nice if you
could contribute a proper test protocol (or even test on some machines)
since you seem to be familiar with those measurements (and I have a very
limited access to x86 gear ... basically just my laptop).

Cheers,
Ben.