47187a4f4f
Previously it was possible for mutex and block profile stack traces to contain up to 32 frames in Stack0 or the resulting pprof profiles. CL 533258 changed this behavior by using some of the space to record skipped frames that are discarded when performing delayed inline expansion. This has lowered the effective maximum stack size from 32 to 27 (the max skip value is 5), which can be seen as a small regression. Add TestProfilerStackDepth to demonstrate the issue and protect all profile types from similar regressions in the future. Fix the issue by increasing the internal maxStack limit to take the maxSkip value into account. Assert that the maxSkip value is never exceeded when recording mutex and block profile stack traces. Three alternative solutions to the problem were considered and discarded: 1) Revert CL 533258 and give up on frame pointer unwinding. This seems unappealing as we would lose the performance benefits of frame pointer unwinding. 2) Discard skipped frames when recording the initial stack trace. This would require eager inline expansion for up to maxSkip frames and partially negate the performance benefits of frame pointer unwinding. 3) Accept and document the new behavior. This would simplify the implementation, but seems more confusing from a user perspective. It also complicates the creation of test cases that make assertions about the maximum profiling stack depth. The execution tracer still has the same issue due to CL 463835. This should be addressed in a follow-up CL. Co-authored-by: Nick Ripley <nick.ripley@datadoghq.com> Change-Id: Ibf4dbf08a5166c9cb32470068c69f58bc5f98d2c Reviewed-on: https://go-review.googlesource.com/c/go/+/586657 Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> |
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README.md
The Go Programming Language
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