@Gilles @Jeff Sorry, I think I replied too quickly. This is what I see if using --bind-to hwthread



This is not what I was after. I only want to use thread 0 of a core ie (cores 0-7), so "cores 192-199" should not have any activity. If I do --bind-to core, the activity jumps from "core 0" to "core 192", and I want to avoid that.

Any other suggestion?

Regards
L
On 08/09/2023 17:53, Jeff Squyres (jsquyres) wrote:
In addition to what Gilles mentioned, I'm curious: is there a reason you have hardware threads enabled?  You could disable them in the BIOS, and then each of your MPI processes can use the full core, not just a single hardware thread.
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*From:* users <users-boun...@lists.open-mpi.org> on behalf of Luis Cebamanos via users <users@lists.open-mpi.org>
*Sent:* Friday, September 8, 2023 7:10 AM
*To:* Ralph Castain via users <users@lists.open-mpi.org>
*Cc:* Luis Cebamanos <luic...@gmail.com>
*Subject:* [OMPI users] Binding to thread 0
Hello,

Up to now, I have been using numerous ways of binding with wrappers (numactl, taskset) whenever I wanted to play with core placing. Another way I have been using is via -rankfile, however I notice that some ranks jump from thread 0 to thread 1 on SMT chips. I can control this with numactl for instance, but it would be great to see similar behaviour when using -rankfile. Is there a way to pack all ranks to one of the threads of each core (preferibly to thread 0) so I can nicely see all ranks with htop on either left or right of the screen?

The command I am using is pretty simple:

mpirun -np $MPIRANKS --rankfile ./myrankfile

and ./myrankfile looks like

rank 33=argon slot=33
rank 34=argon slot=34
rank 35=argon slot=35
rank 36=argon slot=36

Thanks!

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