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

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 05/02/11 09:23, Jan Beulich wrote:
> > > > On 02.05.11 at 08:41, Keir Fraser<keir.xen@xxxxxxxxx>  wrote:
> > 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.
> Correct. I generally found the default threshold of the ondemand
> governor nor very suitable for optimal performance of short lived
> jobs, and boot all of my systems with "cpufreq=xen:ondemand,threshold=20".
Thanks, Keir and Jan! You both helped me a lot!

I think the short term solution for our problem is to disable the cpufreq
governor on our BS2000 machines.

On the long run I'd like to make the cpufreq governor a feature of the
cpupool. This would enable an administrator of a large Xen machine
with a heterogeneous load to specify which domains should run at
full speed and which are allowed to save energy at the cost of latency.

What do you think?


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html


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