[Beowulf] Definition of HPC

Hearns, John john.hearns at mclaren.com
Wed Apr 24 08:38:26 PDT 2013

> Sure, it's important - WITHIN a given job.  Why should a
> new job's performance depend on what ran before?  (And in

I can't see why anyone would want to throw away a performance improvement.

> most cases, the impact is negative, because the cached
> pages are not the ones needed by the new job.)

I may be wrong, but it is not that the cached pages are needed by this job or the last job.
It is that the last job has caused buffer cache to be used, which fills up memory on one or more NUMA nodes.
When the new job starts it allocates memory - if it finds memory is full on one NUMA node you will get NUMA misses,
which lead to slower memory access.

Look at the graph I posted - note that performance CLIMBS when the buffer cache used gets higher - at the point where it overflows
one NUMA node and gets spread about evenly (to my simple understanding)

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