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Subject: Re: [OMPI devel] cpu stride and offset for processor binding
From: Ralph Castain (rhc_at_[hidden])
Date: 2008-02-05 19:25:33

I would think that the syntax being implemented by Voltaire could be
extended to support this need, but I'll leave that up to them for comment.

On 2/5/08 5:01 PM, "Pak Lui" <Pak.Lui_at_[hidden]> wrote:

> Hi all,
> I am trying to implement something in the paffinity:solaris that would
> allow me to specify the cpu id with striding (aka in a sequence) when
> selecting which cpu ids to bind. e.g. For a cpu set that looks like
> this: { 0 1 2 3 4 5 6 7 }, and stride is to 2, and offset is to 1 (which
> means start at pos 1), then ranks will bind to the cpus in the following
> order: { 1 3 5 7 2 4 6 0 }. The obvious intent is to take advantage of
> the perf by allocating the ranks in a certain order on multi-core systems.
> But then we realized this may be implemented elsewhere outside the
> solaris paffinity code. I see something in trac #1023 that may allow me
> to specify a cpuid or cores in a range but it doesn't seem to allow me
> specify the cpu id to bind in strides. And with that, rank specification
> may seem to be doable, but I may end up entering a long list of cpu ids
> in strides manually, if the machine happens to have many cpus. Plus
> another down side is that Solaris doesn't seem to have stable interface
> for me to extract out the core/socket information from the kernel. So
> striding might be the only way for me to go for now.
> Is there some unspoken feature that's coming down the pipe that may
> allow me to specify cpuids in a sequence, or we already have some
> feature like that that I didn't know about? I look around but I don't
> see anything like this.
> Thanks in advance for any comments.