[Beowulf] Theoretical vs. Actual Performance

[Chris Samuel]

On Friday, 23 February 2018 1:45:00 AM AEDT Joe Landman wrote:

> 85% makes the assumption that you have the systems configured in an
> optimal manner, that the compiler doesn't do anything wonky, and that,
> to some degree, you isolate the OS portion of the workload off of most
> of the cores to reduce jitter.   Among other things.

Interesting, purchases I've done before for IB clusters have had Rpeak as 80% 
of Rmax HPL requirement for acceptance testing before and not had much problem 
hitting it.

The worst issue we had was on SandyBridge where the kernel ignoring UEFI 
settings saying "hey, I know these CPUs, I'll enable ALL the power saving" and 
that killed performance until we disabled the states via the kernel boot 
parameters. 

It can be worth running powertop to see what states your CPUs are sitting in 
whilst running HPL, and also "perf top" to see what the system is up to.

Good luck!
Chris
-- 
 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC