[Beowulf] Opinions of Hyper-threading?

[Glen Dosey]

This is just based my experience, and YMMV. I haven't had to deal with
this in quite a while (thank goodness).

In general, if you can guarantee in some fashion that jobs are limited and
bound to the number of real processors available and not HyperThreads,
then there is some (almost immeasurable?) benefit to leaving it on to help
handle the various OS stuff running in the background. If you have a
scheduler assigning jobs based on the how many CPUs a system appears to
have, you will want to turn it off. Basically in my humble opinion, it's
safer and easier to turn off unless you can explicitly state when it will
prove useful and then somehow make it behave in that manner.

Here's a relevant link....
http://softwarecommunity.intel.com/articles/eng/2510.htm


> I inherited a cluster containing a bunch
> of Xeon-based compute nodes. The compute
> nodes were configured with hyper-threading
> turned on. I'm wondering what you HPC cluster
> people think of hyper-threading. I haven't
> heard much about it recently since most
> modern processors are true multi-core.
>
> The main thing I'd like to know is whether
> hyper-threading can do any harm when cpu
> bound jobs are run.
>
> Cordially,
> --
> Jon Forrest
> Research Computing Support
> College of Chemistry
> 173 Tan Hall
> University of California Berkeley
> Berkeley, CA
> 94720-1460
> 510-643-1032
> jlforrest at berkeley.edu
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