Thanks, Hui. What are the values for MPIR_CVAR_CH4_NETMOD? Simply ofi or ucx? Where do I find this information in the manual? Thx...John On 6/22/26 2:50 PM, Zhou, Hui wrote:
[External email - use caution]
* Both |ch4:ucx,ofi| and |ch4:ofi,ucx build with both the UCX and Libfabric, and one can use the environment variable "MPIR_CVAR_CH4_NETMOD" to choose which netmod (ofi or ucx) at runtime.|
The order between ucx an ofi determines the default.
On single mode, shared memory will be used unless it is disabled. "ch4:ucx" disables shared memory by default since UCX's shared memory performance is quite decent. When shared memory is used, which FI_PROVIDER doesn't matter.
Hope this answers your question.
Cheers, Hui ------------------------------------------------------------------------ *From:* John Cary <[email protected]> *Sent:* Monday, June 22, 2026 2:21 PM *To:* [email protected] <[email protected]>; Zhou, Hui <[email protected]> *Subject:* Re: [mpich-discuss] How to get srun/mpich to use the right interface? Hello Hui, We are getting some mysterious results. We have four configurations: --with-device=ch4: ucx --with-device=ch4: ofi --with-device=ch4: ucx,ofi --with-device=ch4: ofi,ucx Is there any difference between the last two? Are the last two valid ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd Hello Hui,
We are getting some mysterious results. We have four configurations:
--with-device=ch4:ucx --with-device=ch4:ofi --with-device=ch4:ucx,ofi --with-device=ch4:ofi,ucx
Is there any difference between the last two? Are the last two valid configurations?
If one is on a single node, does FI_PROVIDER=verbs make any sense? Or perhaps on a single node, shared memory is always used?
Thanks....John
On 6/11/26 10:33 AM, John Cary wrote:
Thanks, Hui!
I am trying to have one build that works for our cluster and also for AWS, which uses ofi. Is that possible?
Thx....John
On 6/11/26 10:06 AM, Zhou, Hui wrote:
[External email - use caution]
HI John,
Try using the UCX instead of libfabric. You can configure MPICH with |./configure --with-device=ch4:ucx| to use UCX. With libfabric, could you try set environment variable |FI_PROVIDER=verbs ?|
If you still have issue, try run a dummy MPI program setting `MPIR_CVAR_DEBUG_SUMMARY=1`. That will provide more logging details on which libfabric provider is being selected.
-- Hui Zhou ------------------------------------------------------------------------ *From:* John Cary via discuss <[email protected]> <mailto:[email protected]> *Sent:* Thursday, June 11, 2026 8:50 AM *To:* [email protected] <mailto:[email protected]> <[email protected]> <mailto:[email protected]> *Cc:* John Cary <[email protected]> <mailto:[email protected]> *Subject:* [mpich-discuss] How to get srun/mpich to use the right interface? How to get mpich to use the right interface? mpich configured and built with libfabric as shown below. It is run using slurm (srun). The result is [1781142435. 559314543] ne07: rank64. vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd How to get mpich to use the right interface?
mpich configured and built with libfabric as shown below. It is run using slurm (srun). The result is
[1781142435.559314543] ne07:rank64.vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation not permitted [1781142435.563376291] ne07:rank66.vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation not permitted Abort(203572367): Fatal error in internal_Init: Other MPI error, error stack ...
which I think means that mpich is txrying to run over the mlx5_0 interface, which does not exist. The interfaces are
eno1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 ib0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 2044 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
and we want to use ib0, infiniband. We tried
export HYDRA_IFACE=ib0 srun ...
and got the same error.
How can srun/mpich be instructed to use the ib0 interface by default?
Also, how can one see which interface mpich is choosing?
Thx...
'/user/builds-linux-centos8-zen2/gvxsimall/mpich-5.0.1/configure' \ --prefix=/home/research/user/installs/linux-centos8-zen2/contrib-gcc1140/mpich-5.0.1-shared \ --enable-shared \ --disable-static \ CC='/home/common/gcc-11.4.0/bin/gcc' \ CXX='/home/common/gcc-11.4.0/bin/g++' \ FC='/home/common/gcc-11.4.0/bin/gfortran' \ F77='/home/common/gcc-11.4.0/bin/gfortran' \ CFLAGS='-pthread -pipe -fPIC' \ CXXFLAGS='-pthread -Wno-deprecated-declarations -pipe -fPIC' \ FFLAGS='-fallow-argument-mismatch -pipe -fPIC' \ FCFLAGS='-fallow-argument-mismatch -pipe -fPIC' \ LDFLAGS='-L/home/common/gcc-11.4.0/lib64 -Wl,-rpath,/home/common/gcc-11.4.0/lib64' \ LDSHARED='-L/home/common/gcc-11.4.0/lib64 -Wl,-rpath,/home/common/gcc-11.4.0/lib64' \ --with-libfabric=install \ --with-device=ch4:ofi \ --without-cuda \ --disable-gl