I'm curious if there are other ideas out there for how to deal with this: From https://bugzilla.redhat.com/show_bug.cgi?id=1965692:I recently acquired a cheap wintel toy tablet/laptop (a Kano PC), which has a Celeron N4000 processor. I tried running HPL benchmarks on it to figure out how fast the thing is. However, xhpl_openmpi crashed with an illegal instruction. I then installed the MPICH version of HPL, and xhpl_mpich runs fine. The issue is
thus in OpenMPI. Looking at the build logs of openmpi-4.1.0-5.fc34.x86_64, I see that it hasbeen compiled with the -mcx16 flag detected by configure. According to the GCC
man page This option enables GCC to generate "CMPXCHG16B" instructions in 64-bit code to implement compare-and-exchange operations on 16-byte aligned 128-bit objects. This is useful for atomic updates of data structures exceeding one machine word in size. The compiler uses this instruction to implement __sync Builtins. However, for __atomic Builtins operating on 128-bit integers, a library call is always used.However, because the instruction is not available on all x86_64 processors, the
use of the flag should be disabled in OpenMPI. ----I filed https://github.com/open-mpi/ompi/issues/9022 and we seem to have the ability to disable this now. Does this seem like the right solution? It does seem a shame to have to cripple the compile though.
There was mention of setting -march - is that appropriate? Thanks, Orion -- Orion Poplawski he/him/his - surely the least important thing about me Manager of NWRA Technical Systems 720-772-5637 NWRA, Boulder/CoRA Office FAX: 303-415-9702 3380 Mitchell Lane orion@xxxxxxxx Boulder, CO 80301 https://www.nwra.com/
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