The --only-ticks-over option is extremely useful, but currently causes the profiler to fall back to the Java implementation. This means some insightful information gets lost, e.g. samples during GC pauses or other native frame information.
Supporting the flag with async-profiler isn't exactly straightforward: By default, async-profiler tries to use a CPUs TSC, which makes it difficult to compare times in the JVM. We can force async-profiler to use the Linux monotonic clock, which is the same as the one used by System.nanoTime() (at least in HotSpot). This allows comparing times and filtering out events that occurred outside of a tick that exceeded the threshold.
As events are only processed later, we need to remember the ticks exceeding the threshold temporarily. As events are processed in order, using a queue makes that pretty simple.
This change also allows using the option together with --alloc.
I tried to make the changes as non-intrusive as possible, but maybe there are cleaner ways in some spots. Let me know if you want me to change something.
The
--only-ticks-overoption is extremely useful, but currently causes the profiler to fall back to the Java implementation. This means some insightful information gets lost, e.g. samples during GC pauses or other native frame information.Supporting the flag with async-profiler isn't exactly straightforward: By default, async-profiler tries to use a CPUs TSC, which makes it difficult to compare times in the JVM. We can force async-profiler to use the Linux monotonic clock, which is the same as the one used by
System.nanoTime()(at least in HotSpot). This allows comparing times and filtering out events that occurred outside of a tick that exceeded the threshold. As events are only processed later, we need to remember the ticks exceeding the threshold temporarily. As events are processed in order, using a queue makes that pretty simple.This change also allows using the option together with
--alloc.I tried to make the changes as non-intrusive as possible, but maybe there are cleaner ways in some spots. Let me know if you want me to change something.