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Re: [Xen-devel] Performance difference between Xen versions

  • To: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
  • From: Keir Fraser <keir.xen@xxxxxxxxx>
  • Date: Mon, 02 May 2011 07:41:06 +0100
  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Sun, 01 May 2011 23:42:14 -0700
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  • Thread-topic: [Xen-devel] Performance difference between Xen versions

On 02/05/2011 06:31, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

>>> Is there any easy explanation for this? Both Xen versions are from SLES
>>> (SLES11 or SLES11 SP1).
>> I think cpufreq handling was off by default in 3.3, and is on by
>> default on 4.0. Try turning this off, or using the performance
>> governor.
> Jan, you got it! With cpufreq=none Xen 4.0 has more or less the same numbers
> as 3.3. Now I wonder why the default is so much slower. I looks as if the
> hypervisor would run at a lower speed. I can't believe it should behave like
> that!

It runs at lower frequency unless your test offers sufficient load over a
long enough time period. Short microbenchmarks are probably finished before
the frequency governor can react.

 -- Keir

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