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Subject: [OMPI users] Specifying slots in rankfile
From: Grzegorz Maj (maju3_at_[hidden])
Date: 2010-06-09 05:45:08

I'd like mpirun to run tasks with specific ranks on specific hosts,
but I don't want to provide any particular sockets/slots/cores.
The following example uses just one host, but generally I'll use more.
In my hostfile I just have:

root_at_host01 slots=4

I was playing with my rankfile to achieve what I've mentioned, but I
always get some problems.

1) With rankfile like:
rank 0=host01 slot=*
rank 1=host01 slot=*
rank 2=host01 slot=*
rank 3=host01 slot=*

I get:

We were unable to successfully process/set the requested processor
affinity settings:

Specified slot list: *
Error: Error

This could mean that a non-existent processor was specified, or
that the specification had improper syntax.
mpirun was unable to start the specified application as it encountered an error:

Error name: Error
Node: host01

when attempting to start process rank 0.
[host01:13715] Rank 0: PAFFINITY cannot get physical processor id for
logical processor 4

I think it tries to find processor #4, bug there are only 0-3

2) With rankfile like:
rank 0=host01 slot=*:*
rank 1=host01 slot=*:*
rank 2=host01 slot=*:*
rank 3=host01 slot=*:*

Everything looks well, i.e. my programs are spread across 4 processors.
But when running MPI program as follows:

MPI::Init(argc, argv);
fprintf(stderr, "after init %d\n", MPI::Is_initialized());
nprocs_mpi = MPI::COMM_WORLD.Get_size();
fprintf(stderr, "won't get here\n");

I get:

after init 1
[host01:14348] *** Process received signal ***
[host01:14348] Signal: Segmentation fault (11)
[host01:14348] Signal code: Address not mapped (1)
[host01:14348] Failing at address: 0x8
[host01:14348] [ 0] [0xffffe410]
[host01:14348] [ 1] p(_ZNK3MPI4Comm8Get_sizeEv+0x19) [0x8051299]
[host01:14348] [ 2] p(main+0x86) [0x804ee4e]
[host01:14348] [ 3] /lib/ [0x4180b5c5]
[host01:14348] [ 4] p(__gxx_personality_v0+0x125) [0x804ecc1]
[host01:14348] *** End of error message ***

I'm using OPEN MPI v. 1.4.2 (downloaded yesterday).
In my rankfile I really want to write something like slot=*. I know
slot=0-3 would be a solution, but when generating rankfile I may not
be sure how many processors are there available on a particular host.

Any help would be appreciated.

Grzegorz Maj