systrap: preserve latency medians across histogram reset - #14426
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sentryOnStubOn saves the stub- and sentry-bound latency medians, then resets both histograms. The sentry fast path check reads from the reset histograms instead of using the saved values, so it always receives zero. Consequently, it cannot disable the sentry fast path when that fast path makes stub latency worse. Pass the saved period medians to shouldDisableSentryFP, as already done for shouldDisableStubFP and in the neighboring state transitions. Fixes: cffce1a ("systrap: Revise slow-path enablement.")
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@konstantin-s-bogom yay or nay? Both Claude and Codex thought this is worth fixing. I will admit that this is AI driven. If slop, feel free to close. |
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No, this is a good fix. It's a pretty bad typo, and could have been causing the sentry FP state to jump around. Thanks!
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sentryOnStubOn records the current stub- and sentry-bound latency medians, then resets both histograms before evaluating the two fast paths. The stub check correctly uses the saved values. The sentry check samples the now-empty histograms again, so it always receives zero and cannot account for the period that just ended. Use the saved period medians for the sentry check too. This matches the other state transitions and ensures both decisions are based on the same completed measurement period. Fixes: cffce1a ("systrap: Revise slow-path enablement.") Tested with: make test TARGETS='//pkg/sentry/platform/systrap:systrap_test' FUTURE_COPYBARA_INTEGRATE_REVIEW=#14426 from ayushr2:codex/fix-systrap-fastpath-median 6172a4b PiperOrigin-RevId: 971361249
copybara-service Bot
pushed a commit
that referenced
this pull request
Aug 26, 2026
sentryOnStubOn records the current stub- and sentry-bound latency medians, then resets both histograms before evaluating the two fast paths. The stub check correctly uses the saved values. The sentry check samples the now-empty histograms again, so it always receives zero and cannot account for the period that just ended. Use the saved period medians for the sentry check too. This matches the other state transitions and ensures both decisions are based on the same completed measurement period. Fixes: cffce1a ("systrap: Revise slow-path enablement.") Tested with: make test TARGETS='//pkg/sentry/platform/systrap:systrap_test' FUTURE_COPYBARA_INTEGRATE_REVIEW=#14426 from ayushr2:codex/fix-systrap-fastpath-median 6172a4b PiperOrigin-RevId: 971361249
copybara-service Bot
pushed a commit
that referenced
this pull request
Aug 26, 2026
sentryOnStubOn records the current stub- and sentry-bound latency medians, then resets both histograms before evaluating the two fast paths. The stub check correctly uses the saved values. The sentry check samples the now-empty histograms again, so it always receives zero and cannot account for the period that just ended. Use the saved period medians for the sentry check too. This matches the other state transitions and ensures both decisions are based on the same completed measurement period. Fixes: cffce1a ("systrap: Revise slow-path enablement.") Tested with: make test TARGETS='//pkg/sentry/platform/systrap:systrap_test' FUTURE_COPYBARA_INTEGRATE_REVIEW=#14426 from ayushr2:codex/fix-systrap-fastpath-median 6172a4b PiperOrigin-RevId: 971361249
copybara-service Bot
pushed a commit
that referenced
this pull request
Aug 26, 2026
sentryOnStubOn records the current stub- and sentry-bound latency medians, then resets both histograms before evaluating the two fast paths. The stub check correctly uses the saved values. The sentry check samples the now-empty histograms again, so it always receives zero and cannot account for the period that just ended. Use the saved period medians for the sentry check too. This matches the other state transitions and ensures both decisions are based on the same completed measurement period. Fixes: cffce1a ("systrap: Revise slow-path enablement.") Tested with: make test TARGETS='//pkg/sentry/platform/systrap:systrap_test' FUTURE_COPYBARA_INTEGRATE_REVIEW=#14426 from ayushr2:codex/fix-systrap-fastpath-median 6172a4b PiperOrigin-RevId: 971361249
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sentryOnStubOn records the current stub- and sentry-bound latency medians,
then resets both histograms before evaluating the two fast paths. The stub
check correctly uses the saved values. The sentry check samples the now-empty
histograms again, so it always receives zero and cannot account for the
period that just ended.
Use the saved period medians for the sentry check too. This matches the
other state transitions and ensures both decisions are based on the same
completed measurement period.
Fixes: cffce1a ("systrap: Revise slow-path enablement.")
Tested with: