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Subject: Re: [OMPI devel] Change in hostfile behavior
From: Tim Mattox (timattox_at_[hidden])
Date: 2008-07-28 12:44:57


My only concern is how will this interact with PLPA.
Say two Open MPI jobs each use "half" the cores (slots) on a
particular node... how would they be able to bind themselves to
a disjoint set of cores? I'm not asking you to solve this Ralph, I'm
just pointing it out so we can maybe warn users that if both jobs sharing
a node try to use processor affinity, we don't make that magically work well,
and that we would expect it to do quite poorly.

I could see disabling paffinity and/or warning if it was enabled for
one of these "fractional" nodes.

On Mon, Jul 28, 2008 at 11:43 AM, Ralph Castain <rhc_at_[hidden]> wrote:
> Per an earlier telecon, I have modified the hostfile behavior slightly to
> allow hostfiles to subdivide allocations.
>
> Briefly: given an allocation, we allow users to specify --hostfile on a
> per-app_context basis. In this mode, the hostfile info is used to filter the
> nodes that will be used for that app_context. However, the prior
> implementation only filtered the nodes themselves - i.e., it was a binary
> filter that allowed you to include or exclude an entire node.
>
> The change now allows you to include a specified #slots for a given node as
> opposed to -all- slots from that node. You are limited to the #slots
> included in the original allocation. I just realized that I hadn't output a
> warning if you attempt to violate this condition - will do so shortly.
> Rather than just abort if this happens, I set the allocation to that of the
> original - please let me know if you would prefer it to abort.
>
> If you have interest in this behavior, please check it out and let me know
> if this meets needs.
>
> Ralph
>
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>

-- 
Tim Mattox, Ph.D. - http://homepage.mac.com/tmattox/
 tmattox_at_[hidden] || timattox_at_[hidden]
 I'm a bright... http://www.the-brights.net/