Fix erratic cycle detector triggering on some Arm systems #3854
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Hi @SeanTAllen, The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do. Release notes are added by creating a uniquely named file in the The basic format of the release notes (using markdown) should be: Thanks. |
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This commit reworks tick usage to be safe with tick values that wrap around. Most of our tick value sources will provide a monotonically increasing value. However, our fallbacks, do not maintain this invariant. They are implemented using clock_gettime and as such, wrap around fairly regularly. They shouldn't wrap around quick enough that they are likely to go around more than once. This PR adds a "difference" function that will get the amount of ticks between compared ticks. Within the runtime ticks are used to set an amount of time to pause when there's no work to do and are used to determine when to run the cycle detector. Prior to this patch, on some Arm hardware, the cycle detector would end up running very infrequently.
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jemc
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Sep 17, 2021
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This commit reworks tick usage to be safe with tick values that wrap around.
Most of our tick value sources will provide a monotonically increasing
value. However, our fallbacks, currently used on non Apple Arm CPUs
do not maintain the invariants.
They are implemented using clock_gettime and as such, wrap around fairly
regularly. They shouldn't wrap around quick enough that they are likely
to go around more than once.
This PR adds a "difference" function that will get the amount of ticks
between compared ticks. Within the runtime ticks are used to set
an amount of time to pause when there's no work to do and are used to
determine when to run the cycle detector.
Prior to this patch, on some Arm hardware, the cycle detector would end up running
very infrequently.