[Beowulf] likwid vs stream (after HPCG discussion)

[Benson Muite]

On 3/19/22 1:28 PM, Mikhail Kuzminsky wrote:
> Just in the HPCG discussion, it was proposed to use the now widely
> used likwid benchmark to estimate memory bandwidth. It gives
> excellent estimates of hardware capabilities.
> 
> Am I right that likwid uses its own optimized assembler code for each
> specific hardware?
likwid has been tuned for some architectures, so can give you some idea 
of achievable performance, where some effort has been made to optimize 
for caches and NUMA effects. It is an open source project where 
community contributions for other architectures are welcome. Of course, 
assembly optimization is not done for all codes, and one needs to rely 
on the compiler in this case.
> 
> If so, it turns out that for the HPC user, stream gives a more
> important estimate - the application is translated by the compiler
> (they do not write in assembler - except for modules from mathematical
> libraries), and stream will give a real estimate of what will be
> received in the application.
This would depend. If a system runs heavily tuned community codes and/or 
uses library routines for the cases for which they are optimized, likwid 
may be better than stream.  If a code that is primarily written for 
portability is used, and is not tuned for the target platform, then 
stream maybe more useful.
> 
> Mikhail Kuzminsky
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