[Beowulf] Benchmark results

Joe Landman landman at scalableinformatics.com
Tue Jan 6 09:10:04 EST 2004

Hi Rene:

  How long were the runs in comparison to the timer resolution?  What 
other processes (if any) were running?  Did various cron-jobs light off 
during any portion of this?

   For opterons, there is an a processor affinity issue whereby you can 
get different performance if the memory allocated and used is not 
associated with that processor.  I have heard that there are patches 
which deal with this, though I haven't had time to try them.  I do seem 
to remember an alignment issue for Xeon as well. 

   I would not expect absolutely identical timing data each time the 
benchmark were run,  but I would expect a tight grouping around a mean 
value.  The relative size of the error would be related to a number of 
factors, including timer resolution, machine state, etc.  For runs of 
reasonable length (longer than 30 minutes), the timer resolution effects 
should be minimal.  If you have other processes lighting off, consuming 
memory, processor cycles, cache, bandwidth, interrupts, it is likely 
that your distribution will reflect this.


Rene Storm wrote:

>Dear cluster folks,
>I saw some weird results of different benchmarks on my systems.
>My problem is to verify these results.
>I've played with hpl benchmark on our clusters (8 CPU Intel, 8 CPU Opteron) and wasn't able to get two times the same result. Of course no configuration changes. Difference round 5-10%.
>So I went down to one machine, but the same behavior.
>Standart mpich, per-complied lapack, two processor on an smp machine.
>10 times the same benchmark gives back 10 different results.
>Same trouble with stream memory benchmark, dgemv matrix calculation and others.
>There was no network, but it was a big installation, so it could be, that there are some running jobs (eg cron-jobs) which disturb my benchmarks results.
>Next Step: I created a self-booting cdrom from the scratch - added litte bit of X and a gui my benchmarks.
>1) cpi - calculating pi with mpich on smp (ch_p4 on loopback)
>2+3) dgemv - 5kx5k matrix calculation , single and smp
>4) crafty chess benchmark - 2 threads
>5) /bin/true - calling true via fork(), taking the time
>6) PMB-MPI1 - Pallas benchmark
>There is only sshd for mpich running, everything is loaded from the cdrom into a ramdisk.
>BUT same result for the results. 5-10% unsteady.
>Please let me know, if you could see same behavior on your machines.
>Does someone know a reason for that?
>If you would like to check this cd out -> 
>40 MB download. You will need at least 512MB and no usb mice, keyboard.
>Thanks in advance
>Rene Storm
>Beowulf mailing list, Beowulf at beowulf.org
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Joseph Landman, Ph.D
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web  : http://scalableinformatics.com
phone: +1 734 612 4615

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