Set OMP_PROC_BIND=false before calling omp_get_max_threads #1241
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
LGTM |
rmjarvis
added
bug report
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Some OMP implemenations have a bug where if omp_get_max_threads() is called (which is what this function does), it sets something called thread affinity.
The upshot of that is that multiprocessing (i.e. not even just omp threading) is confined to a single hardware thread. Yeah, it's idiotic, but that seems to be the case. The only solution found by @erykoff, who looked into it pretty hard, is to set the env variable OMP_PROC_BIND to "false". This seems to stop the bad behavior.
So this PR adds that to the two functions that could potentially call omp_get_max_threads in the C++ layer.