[Beowulf] Hyperthreading and 'OS jitter'

Christopher Samuel samuel at unimelb.edu.au
Tue Aug 1 20:32:23 PDT 2017

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,
 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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