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<p>Thanks Satish, and nice guess for OpenMPI 5 !</p>
<p><br>
</p>
<p>It seems it solves the issue (at least on my GPU box where I reproduced the issue with 8 MPI ranks with OpenMPI 4.x).</p>
<p><br>
</p>
<p>Unhappily, all the clusters we currently use have no module with OpenMPI 5.x. Seems I need to build it to really confirm.</p>
<p><br>
</p>
<p>Probably we will prevent users from configuring our code with OpenMPI-cuda 4.x cause it is really a weird bug.<br>
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<div class="x_PlainText">Pierre LEDAC<br>
Commissariat à l’énergie atomique et aux énergies alternatives<br>
Centre de SACLAY<br>
DES/ISAS/DM2S/SGLS/LCAN<br>
Bâtiment 451 – point courrier n°43<br>
F-91191 Gif-sur-Yvette<br>
+33 1 69 08 04 03<br>
+33 6 83 42 05 79</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>De :</b> Satish Balay <balay.anl@fastmail.org><br>
<b>Envoyé :</b> mardi 17 septembre 2024 15:39:22<br>
<b>À :</b> LEDAC Pierre<br>
<b>Cc :</b> Junchao Zhang; petsc-users; ROUMET Elie<br>
<b>Objet :</b> Re: [petsc-users] [MPI GPU Aware] KSP_DIVERGED</font>
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<div class="PlainText">On Tue, 17 Sep 2024, LEDAC Pierre wrote:<br>
<br>
> Thanks all, I will try and report.<br>
> <br>
> <br>
> Last question, if I use "-use_gpu_aware_mpi 0" flag with a MPI GPU Aware library, do PETSc<br>
> <br>
> disable GPU intra/inter communications and send MPI buffers as usual (with extra Device<->Host copies) ?<br>
<br>
Yes.<br>
<br>
Not: Wrt using MPI that is not GPU-aware - we are changing the default behavior - to not require "-use_gpu_aware_mpi 0" flag.<br>
<br>
<a href="https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/7813__;!!G_uCfscf7eWS!Y40I3F5rvv3KWuJGoo1EdEDq62cnqn2R1Do7WFeicCnNbTaWDHj9SieJOPp2DkxXCkl3iHo8XwantIfdGcpZA8lvcoZH$">https://gitlab.com/petsc/petsc/-/merge_requests/7813</a><br>
<br>
<br>
Satish<br>
<br>
> <br>
> <br>
> Thanks,<br>
> <br>
> <br>
> Pierre LEDAC<br>
> Commissariat à l’énergie atomique et aux énergies alternatives<br>
> Centre de SACLAY<br>
> DES/ISAS/DM2S/SGLS/LCAN<br>
> Bâtiment 451 – point courrier n°43<br>
> F-91191 Gif-sur-Yvette<br>
> +33 1 69 08 04 03<br>
> +33 6 83 42 05 79<br>
> ________________________________<br>
> De : Satish Balay <balay.anl@fastmail.org><br>
> Envoyé : lundi 16 septembre 2024 18:57:02<br>
> À : Junchao Zhang<br>
> Cc : LEDAC Pierre; petsc-users@mcs.anl.gov; ROUMET Elie<br>
> Objet : Re: [petsc-users] [MPI GPU Aware] KSP_DIVERGED<br>
> <br>
> And/Or - try latest OpenMPI [or MPICH] and see if that makes a difference.<br>
> <br>
> --download-mpich or --download-openmpi with latest petsc should build gpu-aware-mpi<br>
> <br>
> Satish<br>
> <br>
> On Mon, 16 Sep 2024, Junchao Zhang wrote:<br>
> <br>
> > Could you try petsc/main to see if the problem persists?<br>
> ><br>
> > --Junchao Zhang<br>
> ><br>
> ><br>
> > On Mon, Sep 16, 2024 at 10:51 AM LEDAC Pierre <Pierre.LEDAC@cea.fr> wrote:<br>
> ><br>
> > > Hi all,<br>
> > ><br>
> > ><br>
> > > We are using PETSc 3.20 in our code and running succesfully several<br>
> > > solvers on Nvidia GPU with OpenMPI library which are not GPU aware (so I<br>
> > > need to add the flag -use_gpu_aware_mpi 0).<br>
> > ><br>
> > ><br>
> > > But now, when using OpenMPI GPU Aware library (OpenMPI 4.0.5 ou 4.1.5 from<br>
> > > NVHPC), some parallel calculations failed with *KSP_DIVERGED_ITS* or<br>
> > > *KSP_DIVERGED_DTOL*<br>
> > ><br>
> > > with several configurations. It may run wells on a small test case with<br>
> > > (matrix is symmetric):<br>
> > ><br>
> > ><br>
> > > *-ksp_type cg -pc_type gamg -pc_gamg_type classical*<br>
> > ><br>
> > ><br>
> > > But suddenly with a number of devices for instance bigger than 4 or 8, it<br>
> > > may fail.<br>
> > ><br>
> > ><br>
> > > If I switch to another solver (BiCGstab), it may converge:<br>
> > ><br>
> > ><br>
> > > *-ksp_type bcgs -pc_type gamg -pc_gamg_type classical*<br>
> > ><br>
> > ><br>
> > > The more sensitive cases where it diverges are the following:<br>
> > ><br>
> > ><br>
> > > *-ksp_type cg -pc_type hypre -pc_hypre_type boomeramg *<br>
> > ><br>
> > > *-ksp_type cg -pc_type gamg -pc_gamg_type classical*<br>
> > ><br>
> > ><br>
> > > And the *bcgs* turnaroud doesn't work each time...<br>
> > ><br>
> > ><br>
> > > It seems to work without problem with aggregation (at least 128 GPUs on my<br>
> > > simulation):<br>
> > ><br>
> > > *-ksp_type cg -pc_type gamg -pc_gamg_type agg*<br>
> > ><br>
> > ><br>
> > > So I guess there is a weird thing happening in my code during the solve in<br>
> > > PETSc with MPI GPU Aware, as all the previous configurations works with non<br>
> > > GPU aware MPI.<br>
> > ><br>
> > ><br>
> > > Here is the -ksp_view log during one fail with the first configuration:<br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > ><br>
> > > *KSP Object: () 8 MPI processes type: cg maximum iterations=10000,<br>
> > > nonzero initial guess tolerances: relative=0., absolute=0.0001,<br>
> > > divergence=10000. left preconditioning using UNPRECONDITIONED norm type<br>
> > > for convergence test PC Object: () 8 MPI processes type: hypre HYPRE<br>
> > > BoomerAMG preconditioning Cycle type V Maximum number of levels<br>
> > > 25 Maximum number of iterations PER hypre call 1 Convergence<br>
> > > tolerance PER hypre call 0. Threshold for strong coupling 0.7<br>
> > > Interpolation truncation factor 0. Interpolation: max elements per<br>
> > > row 0 Number of levels of aggressive coarsening 0 Number of<br>
> > > paths for aggressive coarsening 1 Maximum row sums 0.9 Sweeps<br>
> > > down 1 Sweeps up 1 Sweeps on coarse 1<br>
> > > Relax down l1scaled-Jacobi Relax up<br>
> > > l1scaled-Jacobi Relax on coarse Gaussian-elimination Relax<br>
> > > weight (all) 1. Outer relax weight (all) 1. Maximum size<br>
> > > of coarsest grid 9 Minimum size of coarsest grid 1 Not using<br>
> > > CF-relaxation Not using more complex smoothers. Measure<br>
> > > type local Coarsen type PMIS Interpolation type<br>
> > > ext+i SpGEMM type cusparse linear system matrix = precond<br>
> > > matrix: Mat Object: () 8 MPI processes type: mpiaijcusparse<br>
> > > rows=64000, cols=64000 total: nonzeros=311040, allocated<br>
> > > nonzeros=311040 total number of mallocs used during MatSetValues<br>
> > > calls=0 not using I-node (on process 0) routines*<br>
> > ><br>
> > ><br>
> > > I didn't succeed for the moment creating a reproducer with ex.c examples...<br>
> > ><br>
> > ><br>
> > > Did you see this kind of behaviour before?<br>
> > ><br>
> > > Should I update my PETSc version ?<br>
> > ><br>
> > ><br>
> > > Thanks for any advice,<br>
> > ><br>
> > ><br>
> > > Pierre LEDAC<br>
> > > Commissariat à l’énergie atomique et aux énergies alternatives<br>
> > > Centre de SACLAY<br>
> > > DES/ISAS/DM2S/SGLS/LCAN<br>
> > > Bâtiment 451 – point courrier n°43<br>
> > > F-91191 Gif-sur-Yvette<br>
> > > +33 1 69 08 04 03<br>
> > > +33 6 83 42 05 79<br>
> > ><br>
> ><br>
> <br>
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