-
Notifications
You must be signed in to change notification settings - Fork 1.6k
Fix GEMMT transforming the input array B in some complex cases #5143
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Merged
Merged
Changes from all commits
Commits
File filter
Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
There are no files selected for viewing
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
Oops, something went wrong.
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Outdated suggestions cannot be applied.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.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
@martin-frbg Not sure if I'm interpreting the overall code correctly, but shouldn't B not be written to at all?
While GEMMT is not part of standard BLAS and only exists as an "extension", it does have a definition within MKL, where B is marked as "const". In other words, writing to B should never happen within GEMMT (ie. no in-place operations on B).
https://www.intel.com/content/www/us/en/docs/onemkl/developer-reference-c/2025-0/cblas-gemmt.html
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Technically the promise is only that the inputs will be unchanged on exit, IMHO what happens behind closed doors is implementation-defined. And the current implementation is inefficient and needs to be redone eventually. It was only a quick, GEMV-based hack to provide any support for GEMMT at all when the Reference implementation did not yet have it.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Agree that it's better to have something rather than nothing. Looking purely at the implementation side, writing to B would still be ill-advised as it's promised as "const" by MKL. One possible case is that B is shared with another thread (say in a non-OpenBLAS function), which expects it unchanged. There may also be a possible performance degradation due to cache pollution stemming from unnecessary writes to B.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
As I say the entire implementation is an ugly hack and needs to be replaced - but that is another can of worms, namely #4921, and I can only do so much in a day (and sometimes not even that)
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
https://xkcd.com/2347/