[Beowulf] likwid vs stream (after HPCG discussion)

[Mikhail Kuzminsky]

In message from Scott Atchley <e.scott.atchley at gmail.com> (Sun, 20 Mar
2022 14:52:10 -0400):
> On Sat, Mar 19, 2022 at 6:29 AM Mikhail Kuzminsky <kus at free.net> 
>wrote:
> 
>> 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.
>>
> 
> When vendors advertise STREAM results, they compile the application 
>with
> non-temporal loads and stores. This means that all memory accesses 
>bypass
> the processor's caches. If your application of interest does a random 
>walk
> through memory and there is neither temporal or spatial locality, 
>then
> using non-temporal loads and stores makes sense and STREAM 
>irrelevant.

STREAM is not initially oriented to random access to memory. In this
case, memory latencies are important, and it makes more sense to get a
bandwidth estimate in the mega-sweep
(https://github.com/UK-MAC/mega-stream).