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Performance issues with memory/patcher #5763

Open mkre opened 6 years ago

mkre commented 6 years ago

Background information

What version of Open MPI are you using? (e.g., v1.10.3, v2.1.0, git branch name and hash, etc.)

v3.1.2

Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)

Built from source tarball

Please describe the system on which you are running

Details of the problem

I am currently evaluating the performance of Open MPI 3.1.2 and came across what seems like performance issues with the memory/patcher component. In fact, enabling this component has negative impact on performance for our CFD code. It's not a big difference at small scales, but it is reproducible and it gets amplified at larger core counts. The typical penalty I have observed is in the range of 1-5%. This raises two questions:

  1. What could be the reason for the negative performance impact of the memory/patcher component?
  2. Is it safe to disable the patcher component or are there any possible negative implications? Note that we are building Open MPI specifically for this code, so we could live with some restrictions in that regard.

Please let me know if you need further information, like micro-benchmark results or log outputs.

Thanks, Moritz

mkre commented 6 years ago

I did some further testing and have not observed any issues with disabled memory patcher so far, but I'd still appreciate knowing what this component does (and whether it's safe to disable it) and why it worsens the performance in my case.