IssueTracker

After turning method tracing on in microbench by default in all cases, we have over time found multiple issues where runtime performance is drastically reduced after capturing a method trace, depending on OS version and ART mainline version.

• API 34 or certain mainline releases: Method tracing disables AOT compilation, observable JIT. b/303660864
• API 26-30: Method tracing regresses performance, but without observable JIT. b/313868903
• API 21: Method tracing corrupts stack. b/300658578

We also found that it was necessary to suppress method traces on long running benchmarks to avoid ANRs, as even a single loop of a compose benchmark can take several seconds to trace. This made numbers and tracing behavior both less predictable, because duration of benchmark now defines whether it gets a method trace, since it's used to predict if simply taking a method trace on the UI thread will cause an ANR. See b/311412125

Currently, method tracing is off by default, everywhere, we want to turn it back on safely.

Tasks:

• Enable method tracing by default only on certain OS and ART mainline versions
• Add a warning when method tracing can't be enabled safely, with suggestion of what to do
• Throw rather than capture invalid data (similar to the old startup microbench mode)