[Beowulf] Hyperthreading and 'OS jitter'

[Evan Burness]

Thanks for the history lessons, Chris! Very interesting indeed.

Would be interesting to take it a step further and measure what the impacts
(good, bad, or otherwise) of picking a specific core on a given CPU uArch
layout for the OS.


Cheers,

Evan

On Tue, Aug 1, 2017 at 10:32 PM, Christopher Samuel <samuel at unimelb.edu.au>
wrote:

> On 26/07/17 00:31, Evan Burness wrote:
>
> > If I recall correctly, IBM did just what you're describing with the
> > BlueGene CPUs. I believe those were 18-core parts, with 2 of the cores
> > being reserved to run the OS and as a buffer against jitter. That left a
> > nice, neat power-of-2 amount of cores for compute tasks.
>
> Close, but the 18 cores were for yield, with 1 core of running the
> Compute Node Kernel (CNK) and 16 cores for the task that the CNK would
> launch. The 18th was inaccessible.
>
> But yes, I think SGI (RIP) pioneered this on Intel with their Altix
> systems and was the reason they wrote the original cpuset code in the
> Linux kernel so they could constrain a set of cores for the boot
> services and the rest were there to run jobs on.
>
> All the best,
> Chris
> --
>  Christopher Samuel        Senior Systems Administrator
>  Melbourne Bioinformatics - The University of Melbourne
>  Email: samuel at unimelb.edu.au Phone: +61 (0)3 903 55545
>
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-- 
Evan Burness
Director, HPC Solutions
Cycle Computing
evan.burness at cyclecomputing.com
(919) 724-9338
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