Yeah, as Wesley suggested, it will shed more light if you try set the environment variable MPIR_CVAR_CH4_OFI_CAPABILITY_SETS_DEBUG and get some diagnostics. We haven’t tested against such old libfabric for a while so some discrepancy in the capability set may have crept in.

-- 
Hui Zhou

From: Bland, Wesley via discuss <discuss@mpich.org>
Date: Wednesday, June 16, 2021 at 8:47 AM
To: Antonio J. Peña <antonio.pena@bsc.es>
Cc: Bland, Wesley <wesley.bland@intel.com>, MPICH Discuss <discuss@mpich.org>
Subject: Re: [mpich-discuss] libfabric+psm2 performance

If you set the environment variable MPIR_CVAR_CH4_OFI_CAPABILITY_SETS_DEBUG, it will print out the capability set (and provider) that MPICH is using so you can confirm.