[3.14] gh-144438: Fix false sharing between QSBR and tlbc_index (gh-144554)#144923
Merged
colesbury merged 3 commits intopython:3.14from Mar 31, 2026
Merged
[3.14] gh-144438: Fix false sharing between QSBR and tlbc_index (gh-144554)#144923colesbury merged 3 commits intopython:3.14from
colesbury merged 3 commits intopython:3.14from
Conversation
…pythongh-144554) Align the QSBR thread state array to a 64-byte cache line boundary and add padding at the end of _PyThreadStateImpl. Depending on heap layout, the QSBR array could end up sharing a cache line with a thread's tlbc_index, causing QSBR quiescent state updates to contend with reads of tlbc_index in RESUME_CHECK. This is sensitive to earlier allocations during interpreter init and can appear or disappear with seemingly unrelated changes. Either change alone is sufficient to fix the specific issue, but both are worthwhile to avoid similar problems in the future. (cherry picked from commit 6577d87) Co-authored-by: Sam Gross <colesbury@gmail.com>
colesbury
requested review from
encukou and
ericsnowcurrently
as code owners
Contributor
Author
|
Added @hugovk for |
Member
|
Okay to merge for 3.14, please resolve conflicts. |
This file contains hidden or 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
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
Align the QSBR thread state array to a 64-byte cache line boundary and add padding at the end of _PyThreadStateImpl. Depending on heap layout, the QSBR array could end up sharing a cache line with a thread's tlbc_index, causing QSBR quiescent state updates to contend with reads of tlbc_index in RESUME_CHECK. This is sensitive to earlier allocations during interpreter init and can appear or disappear with seemingly unrelated changes.
Either change alone is sufficient to fix the specific issue, but both are worthwhile to avoid similar problems in the future. (cherry picked from commit 6577d87)
Tools/ftscalingbench/ftscalingbench.pygenerator #144438