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Subject: Re: [OMPI devel] Revise paffinity method?
From: Terry Dontje (Terry.Dontje_at_[hidden])
Date: 2009-05-08 06:35:37


So in essence the user might set one parameter and depending on whether
orted is being used to launch the job or not determines when the process
binding happens (process launch vs MPI_Init time). In the case that one
needs/wants to rely on a different launcher to bind then you don't
specify the OMPI parameter at all.

Is that right?

So, will there be a way to force MPI_Init based binding even if one is
using orted to launch a job. Not sure there really is a use case for
such just curious.

--td

Ralph Castain wrote:
> FWIW: Jeff and I chatted about this on the phone and came up with two
> issues that need resolving:
>
> 1. we use mpi_paffinity_alone to indicate that we should bind
> processes, yet the orteds have no way of seeing that MCA param as it
> is registered and evaluated in the MPI layer. We propose to resolve
> this by (a) declaring an opal_paffinity_alone MCA param in the
> paffinity framework, and then (b) declaring an alias of
> mpi_paffinity_alone for it, also in the paffinity framework. This
> obviously is an abstraction break, but we feel it is an acceptable one
> under the circumstances.
>
> Our apologies to Lenny, whose ears were boxed over doing just this
> last year...sigh.
>
> This will allow the orteds to check to see if processes should be
> bound before launching them.
>
> 2. we would not be able to bind processes launched without daemons
> under systems that do not provide their own process binding
> capability. For example, on Torque, we have an ability to natively
> launch processes from within mpirun - those processes currently can
> bind themselves in MPI_Init, but would not be able to do so any longer
> under this proposed change.
>
> To alleviate that problem, we propose to leave the process binding
> code that is currently in MPI_Init, but surround it with a test to see
> if an MCA param has been set indicating that the proc is to use that
> code to bind itself. Thus, when launching without daemons (but via
> mpirun), we can set the flag and instruct the procs to bind
> themselves. However, procs that are launched without daemons via
> something which has its own binding capability (e.g., SLURM), and
> procs that were launched via daemon (and hence would have already been
> bound), would not attempt to do so.
>
>
> Any further thoughts are welcome...
> Ralph
>
>
> On May 7, 2009, at 12:59 PM, Ralph Castain wrote:
>
>> I can do the coding - just want to ensure interested others get their
>> $0.002 in on how it should work.
>>
>> I came up with a way to do it that doesn't require changes to the
>> paffinity framework. I can complete the prototype next week on an hg
>> branch and let you look at it. Mostly consists of moving what is now
>> in MPI_Init into the odls modules between the fork and exec, as Brian
>> suggested.
>>
>>
>> On May 7, 2009, at 12:43 PM, Terry Dontje wrote:
>>
>>> Brian W. Barrett wrote:
>>>> On Wed, 6 May 2009, Ralph Castain wrote:
>>>>
>>>>> Any thoughts on this? Should we change it?
>>>>
>>>> Yes, we should change this (IMHO) :).
>>>>
>>> Me too.
>>>>> If so, who wants to be involved in the re-design? I'm pretty sure
>>>>> it would require some modification of the paffinity framework,
>>>>> plus some minor mods to the odls framework and (since you cannot
>>>>> bind a process other than yourself) addition of a new small
>>>>> "proxy" script that would bind-then-exec each process started by
>>>>> the orted (Eugene posted a candidate on the user list, though we
>>>>> will have to deal with some system-specific issues in it).
>>>>
>>>> I can't contribute a whole lot of time, but I'd be happy to lurk,
>>>> offer advice, and write some small bits of code. But I definitely
>>>> can't lead.
>>>>
>>>> Fist offering of opinion from me. I think we can avoid the "proxy"
>>>> script by doing the binding after the fork but before the exec.
>>>> This will definitely require minor changes to the odls and probably
>>>> a bunch of changes to the paffinity framework. This will make
>>>> things slightly less fragile than a script would, and yet get us
>>>> what we want.
>>> I'll have to talk with Len to see if Sun has any time to allocate to
>>> this.
>>>
>>> --td
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>
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