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Subject: Re: [OMPI users] Ensuring use of real cores
From: John R. Cary (cary_at_[hidden])
Date: 2012-09-12 07:57:36

I do want in fact to bind first to one HT of each core
before binding to two HTs of one core. So that will
be possible in 1.7?


On 9/11/12 11:19 PM, Ralph Castain wrote:
> 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.
> 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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