[Beowulf] NUMA info request

[Eric Thibodeau]

Mark,

    NUMA is an acronym meaning Non Uniform Memory Access. This is a 
hardware constraint and is not a "performance" switch you turn on. Under 
the Linux kernel there is an option that is meant to tell the kernel to 
be conscious about that hardware fact and attempt to help it optimize 
the way it maps the memory allocation to a task Vs the processor the 
given task will be using (processor affinity, check out taskset (in 
recent util-linux implementations, ie: 2.13+).

    In your specific case, you would have 4Gigs per CPU and would want 
to make sure each task (assuming one per CPU) stays on the same CPU all 
the time and would want to make sure each task fits within the "local" 4Gig.

Here is a link that should help you out with that respect:

http://www.nic.uoregon.edu/tau-wiki/Guide:Opteron_NUMA_Analysis

Eric

Mark Kosmowski wrote:
> Could someone please provide a website or two for NUMA information?
> I'm about to upgrade the RAM of my cluster and might want to
> experiment with using NUMA to try too eek out a little speed.  I am
> definitely more of a cluster end-user than a developer, so NUMA admin
> / usage sites would be preferred to development sites.
>
> Thanks!
>
> (My background: Chemistry graduate student using plane wave software,
> 3 node dual cpu single-core opteron cluster soon to each have 8 Gb RAM
> on Linux (OpenSUSE 10.2 / 64 bit) with OpenMPI.)
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