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Subject: Re: [OMPI devel] problem when binding to socket on a single socket node
From: Ralph Castain (rhc_at_[hidden])
Date: 2010-04-09 12:08:33


Okay, just wanted to ensure everyone was working from the same base code.

Terry, Brad: you might want to look this proposed change over. Something doesn't quite look right to me, but I haven't really walked through the code to check it.

On Apr 9, 2010, at 9:33 AM, Terry Dontje wrote:

> Nadia Derbey wrote:
>>
>> On Fri, 2010-04-09 at 08:41 -0600, Ralph Castain wrote:
>>
>>> Just to check: is this with the latest trunk? Brad and Terry have been making changes to this section of code, including modifying the PROCESS_IS_BOUND test...
>>>
>>>
>>>
>>
>> Well, it was on the v1.5. But I just checked: looks like
>> 1. the call to OPAL_PAFFINITY_PROCESS_IS_BOUND is still there in
>> odls_default_fork_local_proc()
>> 2. OPAL_PAFFINITY_PROCESS_IS_BOUND() is defined the same way
>>
>> But, I'll give it a try with the latest trunk.
>>
>> Regards,
>> Nadia
>>
>>
> The changes, I've done do not touch OPAL_PAFFINITY_PROCESS_IS_BOUND at all. Also, I am only touching code related to the "bind-to-core" option so I really doubt if my changes are causing issues here.
>
> --td
>>> On Apr 9, 2010, at 3:39 AM, Nadia Derbey wrote:
>>>
>>>
>>>> Hi,
>>>>
>>>> I am facing a problem with a test that runs fine on some nodes, and
>>>> fails on others.
>>>>
>>>> I have a heterogenous cluster, with 3 types of nodes:
>>>> 1) Single socket , 4 cores
>>>> 2) 2 sockets, 4cores per socket
>>>> 3) 2 sockets, 6 cores/socket
>>>>
>>>> I am using:
>>>> . salloc to allocate the nodes,
>>>> . mpirun binding/mapping options "-bind-to-socket -bysocket"
>>>>
>>>> # salloc -N 1 mpirun -n 4 -bind-to-socket -bysocket sleep 900
>>>>
>>>> This command fails if the allocated node is of type #1 (single socket/4
>>>> cpus).
>>>> BTW, in that case orte_show_help is referencing a tag
>>>> ("could-not-bind-to-socket") that does not exist in
>>>> help-odls-default.txt.
>>>>
>>>> While it succeeds when run on nodes of type #2 or 3.
>>>> I think a "bind to socket" should not return an error on a single socket
>>>> machine, but rather be a noop.
>>>>
>>>> The problem comes from the test
>>>> OPAL_PAFFINITY_PROCESS_IS_BOUND(mask, &bound);
>>>> called in odls_default_fork_local_proc() after the binding to the
>>>> processors socket has been done:
>>>> ========
>>>> <snip>
>>>> OPAL_PAFFINITY_CPU_ZERO(mask);
>>>> for (n=0; n < orte_default_num_cores_per_socket; n++) {
>>>> <snip>
>>>> OPAL_PAFFINITY_CPU_SET(phys_cpu, mask);
>>>> }
>>>> /* if we did not bind it anywhere, then that is an error */
>>>> OPAL_PAFFINITY_PROCESS_IS_BOUND(mask, &bound);
>>>> if (!bound) {
>>>> orte_show_help("help-odls-default.txt",
>>>> "odls-default:could-not-bind-to-socket", true);
>>>> ORTE_ODLS_ERROR_OUT(ORTE_ERR_FATAL);
>>>> }
>>>> ========
>>>> OPAL_PAFFINITY_PROCESS_IS_BOUND() will return true if there bits set in
>>>> the mask *AND* the number of bits set is lesser than the number of cpus
>>>> on the machine. Thus on a single socket, 4 cores machine the test will
>>>> fail. While on other the kinds of machines it will succeed.
>>>>
>>>> Again, I think the problem could be solved by changing the alogrithm,
>>>> and assuming that ORTE_BIND_TO_SOCKET, on a single socket machine =
>>>> noop.
>>>>
>>>> Another solution could be to call the test
>>>> OPAL_PAFFINITY_PROCESS_IS_BOUND() at the end of the loop only if we are
>>>> bound (orte_odls_globals.bound). Actually that is the only case where I
>>>> see a justification to this test (see attached patch).
>>>>
>>>> And may be both solutions could be mixed.
>>>>
>>>> Regards,
>>>> Nadia
>>>>
>>>>
>>>> --
>>>> Nadia Derbey <Nadia.Derbey_at_[hidden]>
>>>> <001_fix_process_binding_test.patch>_______________________________________________
>>>> devel mailing list
>>>> devel_at_[hidden]
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>>>
>>> _______________________________________________
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>>>
>>>
>
>
> --
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