Isn't this a case for --map-by core --bind-to hwthread? Because you want to map each 
process by core but bind the the first hwthread.From the looks of it your process is 
both binding and mapping by hwthread now. -NathanOn Sep 11, 2023, at 10:20 AM, Luis 
Cebamanos via users <users@lists.open-mpi.org> wrote:@Gilles @Jeff Sorry, I 
think I replied too quickly. This is what I
   see if using --bind-to hwthread  <Z9k0wIPYngd30f0X.png>   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.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 likerank 33=argon 
slot=33 rank 34=argon slot=34 rank 35=argon slot=35 rank 36=argon slot=36Thanks!

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