Closed
Description
Thank you for taking the time to submit an issue!
Background information
I am looking at a system which is showing very poor performance with some applications (notably OpenFOAM) when running Open MPI. The system in question has busy polling enabled to (in theory) improve message latency:
==> /proc/sys/net/core/busy_poll <==
50
==> /proc/sys/net/core/busy_read <==
50
What version of Open MPI are you using? (e.g., v3.0.5, v4.0.2, git branch name and hash, etc.)
v4.1.x, main, etc
Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)
Both from release tarball and git checkout.
If you are building/installing from a git clone, please copy-n-paste the output from git submodule status.
Please describe the system on which you are running
- Operating system/version: Linux 3.10.0-1160.76.1.el7.x86_64
- Computer hardware: Intel Xeon
- Network type: 100 GigE
Details of the problem
With these settings we see a 3-5x slowdown in the performance of all steps of OpenFOAM motorbike (can give run details if requested) vs with them both set to 0 (busy waiting disabled).
Without busy polling:
Finished meshing in = 24.9 s
ExecutionTime = 41.7 s ClockTime = 44 s
With busy polling:
Finished meshing in = 73.02 s.
ExecutionTime = 109.37 s ClockTime = 112 s
The only difference between these runs is busy polling enabled vs disabled.