Improvements to HWPMC support on FreeBSD/arm64 to handle counter wraparound
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Authored by rwatson on Jan 3 2021, 9:27 PM.

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Reviewers

andrew
br
gnn

Summary

Starting with a patch from Andrew Turner and Ruslan Bukin to improve HWPMC support for ARMv8-A counter wraparound:

Move to per-CPU overflow entries, since we model these as 32-bit extensions to 32-bit per-CPU registers.

Attempt to address a race between overflow counting and overflows, which may occur (for example) if the overflow happens while interrupts are off during context switching.

With these changes, I no longer experience panics when using per-process
counters on a multithreaded process.

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Repository

rS FreeBSD src repository - subversion

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Buildable 35913
Build 32802: arc lint + arc unit

Event Timeline

rwatson created this revision.Jan 3 2021, 9:27 PM

Herald added subscribers: emaste, imp. · View Herald TranscriptJan 3 2021, 9:27 PM

rwatson requested review of this revision.Jan 3 2021, 9:27 PM

Harbormaster completed remote builds in B35913: Diff 81596.Jan 3 2021, 9:27 PM

rwatson retitled this revision from Starting with a patch from Andrew Turner and Ruslan Bukin to improve HWPMC support for ARMv8-A counter wraparound: to Starting with a patch from Andrew Turner and Ruslan Bukin to improve HWPMCsupport for ARMv8-A counter wraparound:.Jan 3 2021, 9:28 PM

rwatson changed the repository for this revision from rS FreeBSD src repository - subversion to rG FreeBSD src repository.

rwatson added a project: arm64.

rwatson retitled this revision from Starting with a patch from Andrew Turner and Ruslan Bukin to improve HWPMCsupport for ARMv8-A counter wraparound: to Improvements to HWPMC support on FreeBSD/arm64 to handle counter wraparound.

rwatson edited the summary of this revision. (Show Details)

andrew added inline comments.Jan 4 2021, 9:48 AM