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 <[email protected]> Date: Wednesday, June 16, 2021 at 8:47 AM To: Antonio J. Peña <[email protected]> Cc: Bland, Wesley <[email protected]>, MPICH Discuss <[email protected]> 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.