On s390x, use the stckf instruction to get the cycles timer value. #499
Conversation
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
The test ut0rnd.random_from_interval_fast from test suite merge_innodb_tests-t is failing on s390x because the stck (Store Clock) instruction in the my_timer_cycles() function is not very good when used as a source of randomness in random_64_fast(). The stckf (Store Clock Fast) instruction works much better as a source of randomness and is less expensive to call as well. Compared to stck, stckf may store the same clock value twice but according to the Additional Comments comment in mysys/my_rdtsc.cc that should be fine. All 'make test' tests pass with this change. The stckf instruction was added to the Z Architecture in z9 and all of the s390x versions of distros MySQL supports are compiled for z9 or newer so we don't need to check if it is available.
|
Hi, thank you for your contribution. Please confirm this code is submitted under the terms of the OCA (Oracle's Contribution Agreement) you have previously signed by cutting and pasting the following text as a comment: |
|
I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it. |
|
Hi, thank you for your contribution. Your code has been assigned to an internal queue. Please follow |
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Outdated suggestions cannot be applied.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.
The test ut0rnd.random_from_interval_fast from test suite merge_innodb_tests-t is failing on s390x on 8.0.34 because the stck (Store Clock) instruction in the my_timer_cycles() function is not very good when used as a source of randomness in random_64_fast().
The stckf (Store Clock Fast) instruction works much better as a source of randomness and is less expensive to call as well. Compared to stck, stckf may store the same clock value twice but according to the Additional Comments comment in mysys/my_rdtsc.cc that should be fine. All 'make test' tests pass with this change.
The stckf instruction was added to the Z Architecture in z9 and all of the s390x versions of distros MySQL supports are compiled for z9 or newer so we don't need to check if it is available.