Ok thanks all, so with Satish test, we know it is MPI_Init call from PetscInitialize.
Probably, as Matt said, something related to gethostbyname() ... I will do some other test, contact MPICH support and will report any workaround, Thanks again for your reactivity ! Pierre LEDAC Commissariat à l’énergie atomique et aux énergies alternatives Centre de SACLAY DES/ISAS/DM2S/STMF/LGLS Bâtiment 451 – point courrier n°43 F-91191 Gif-sur-Yvette +33 1 69 08 04 03 +33 6 83 42 05 79 ________________________________ De : Satish Balay <ba...@mcs.anl.gov> Envoyé : mercredi 27 juillet 2022 18:57:16 À : LEDAC Pierre Cc : petsc-dev@mcs.anl.gov Objet : Re: [petsc-dev] [Minor issue] Lag during PetscInitialize on Fedora 36 (never seen before with other OS) I'm seeing this behavior on a laptop - but not desktop [both F36] (with both mpich and openmpi buids) >>>> laptop/mpich <<<< balay@p1 /home/balay/petsc/src/ksp/ksp/tests (main =) $ sleep 30; time ./ex39; time ./ex39 real 0m1.709s user 0m0.079s sys 0m0.042s real 0m0.116s user 0m0.077s sys 0m0.014s <<<< However --with-mpi=0 is fine >>>> balay@p1 /home/balay/petsc/src/ksp/ksp/tests (main =) $ sleep 30; time ./ex39; time ./ex39 real 0m0.116s user 0m0.108s sys 0m0.008s real 0m0.081s user 0m0.072s sys 0m0.008s <<<<< Here is the desktop run (with mpich) >>> [balay@pj01 tests]$ sleep 30; time ./ex39; time ./ex39 real 0m0.065s user 0m0.033s sys 0m0.019s real 0m0.053s user 0m0.029s sys 0m0.013s <<<< And --with-mpi=0 >>> [balay@pj01 tests]$ sleep 30; time ./ex39; time ./ex39 real 0m0.087s user 0m0.046s sys 0m0.015s real 0m0.024s user 0m0.018s sys 0m0.006s <<< But don't know why its behaving this way [on the laptop] Satish On Wed, 27 Jul 2022, LEDAC Pierre wrote: > Hello, > > > Recently migrated from Fedora34 to Fedora36, using PETSc I have some lag > during the PetscInitialize, which > > disappeared if I run again immediately the binary. But after few seconds, the > lag happens again (see below). > > > I suspected MPICH 4.0.2 on Fedora36, but a small reproducer indicated the > issue is not in MPI_Init but really during PetscInitialize > > > Just annoying during testing, not very important, but did someone already see > this ? > > > Thanks, > > > portable: /volatile/ledacp/petsc/src/ksp/ksp/tests (main) > time ./ex39 > > real 0m3,593s > user 0m0,872s > sys 0m0,433s > portable: /volatile/ledacp/petsc/src/ksp/ksp/tests (main) > time ./ex39 > > real 0m0,310s > user 0m0,884s > sys 0m0,023s > > # Wait ~20 seconds then again: > > portable: /volatile/ledacp/petsc/src/ksp/ksp/tests (main) > time ./ex39 > > real 0m3,507s > user 0m0,897s > sys 0m0,025s > portable: /volatile/ledacp/petsc/src/ksp/ksp/tests (main) > time ./ex39 > > real 0m0,154s > user 0m0,725s > sys 0m0,015s > portable: /volatile/ledacp/petsc/src/ksp/ksp/tests (main) > time ./ex39 > > real 0m0,176s > user 0m0,875s > sys 0m0,021s > > > > Pierre LEDAC > Commissariat à l’énergie atomique et aux énergies alternatives > Centre de SACLAY > DES/ISAS/DM2S/STMF/LGLS > Bâtiment 451 – point courrier n°43 > F-91191 Gif-sur-Yvette > +33 1 69 08 04 03 > +33 6 83 42 05 79 >