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Subject: Re: [OMPI devel] New mapper module
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-04-17 10:14:41


Sweet!

On Apr 17, 2008, at 10:06 AM, Ralph H Castain wrote:
> I have implemented and committed (r18190) a new RMAPS module that
> sequentially maps ranks to the hosts listed in a hostfile. You must
> set -mca
> rmaps seq in order to access this module - it will -not- be selected
> any
> other way.
>
> The basic method of operation respects the hostfile descriptions on
> the wiki
> page, but I will describe it here briefly as well:
>
> 1. if we are in a managed environment, we will only map to nodes
> within the
> allocation. If your hostfile contains nodes outside the allocation,
> we will
> report an error and abort. So if you want to map ranks sequentially,
> you
> need to be sure that the hostfile describing this mapping contains
> only
> hosts that -can- be mapped. In an unmanaged environment, we
> automatically
> include all the nodes in any specified hostfiles, so this won't be a
> problem.
>
> 2. if you specify a default-hostfile, we will use it - however, any
> hostfiles specified for an app_context will override the default-
> hostfile.
> Any apps that do -not- have a hostfile specified will be mapped
> sequentially
> to the hosts in the default-hostfile
>
> 3. if your app_context does not specify a number of procs, we will
> automatically map one proc to each and every entry in the hostfile
>
> 4. if your app_context does specify a number of procs, we will
> sequentially
> map that number of procs, one to each entry in the hostfile. Multiple
> app_contexts are supported, with the sequence continuing across the
> app_contexts.
>
> 5. if you specify a number of procs greater than the number of
> entries in
> your hostfile, we will map the overrun using byslot rules - i.e., we
> will
> start by filling the remaining slots on the first node in your
> hostfile,
> then proceed to fill the second node in your hostfile, etc.
>
> 6. if your allocation does not permit oversubscription, we will
> report an
> error and abort if you attempt to place more procs on a node than
> slots.
>
> Hope that helps
> Ralph
>
>
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-- 
Jeff Squyres
Cisco Systems