Re: Performance difference between Xen versions

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 05/02/11 09:23, Jan Beulich wrote:
>>>> On 02.05.11 at 08:41, Keir Fraser<keir.xen@gmail.com>  wrote:
>> On 02/05/2011 06:31, "Juergen Gross"<juergen.gross@ts.fujitsu.com>  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
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