Re: [Xen-devel] compute performace problem

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 23 Apr 2005, at 15:52, David Becker wrote:

> One of my users discovered large deviations in execution time for his
> mpi jobs on xenUs.  I can reproduce the problem running his job on
> a single VM.  On a native linux box the job completes in 64 secs +/-
> a second or so.  On a xenU, it completes somewhere between 64 and 250
> secs.  This is true on 2.0.5 (2.6.10-xenU) and 
> 2.0-testing(2.6.11-xenU).
> I tried xen-unstable but it seemed any task was taking 4 times as
> long as on 2.0 so I guess its still too unstable.
>
> Any suggestions I can try?
Does the domU have the same amount of memory as the native Linux? Is 
the native Linux running on a single cpu, just like the domU? Is the 
domU definitely quiescent apart from the mpi job? Have you actually 
directly observed the app taking 250 seconds, or are you relying on 
wall-clock time within the domU (it would be very odd if its time was 
so badly wrong, but this sounds like a very odd situation).
If the app is cpu-bound, there are no other apps running in the domain, 
and no other domains contending for that cpu, then it is hard to 
imagine where the slowdown coudl come from.
 -- Keir


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