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Subject: Re: [OMPI users] Ensuring use of real cores
From: Ralph Castain (rhc_at_[hidden])
Date: 2012-09-11 23:19:31


Not entirely sure I know what you mean. If you are talking about running without specifying binding, then it makes no difference - we'll run wherever the OS puts us, so you would need to tell the OS not to use the virtual cores (i.e., disable HT).

If you are talking about binding, then pre-1.7 releases all bind to core at the lowest level. On a hyperthread-enabled machine, that binds you to both HT's of a core. Starting with the upcoming 1.7 release, you can bind to the separate HTs, but that doesn't sound like something you want to do.

HTH
Ralph

On Sep 11, 2012, at 6:34 PM, John R. Cary <cary_at_[hidden]> wrote:

> Our code gets little benefit from using virtual cores (hyperthreading),
> so when we run with mpiexec on an 8 real plus 8 virtual machine, we
> would like to be certain that it uses only the 8 real cores.
>
> Is there a way to do this with openmpi?
>
> Thx....John
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