On Thu, 26 Oct 2023 20:33:31 GMT, Man Cao <m...@openjdk.org> wrote: >> @albertnetymk, the hsperf counters are a non-public API and the new counters >> have been added to the non-standard `sun.threads.cpu_time` name space which >> is "[unstable and >> unsupported](https://github.com/openjdk/jdk/blob/9864951dceb0ddc4479ced04b6d5a2363f1e307d/src/hotspot/share/runtime/perfData.cpp#L56)" >> so I don't think a CSR is required. > >> Is there some overlapping btw this and the existing _vtime_accum. If so, can >> they be consolidated somehow? > > We don't really like `_vtime_accum` for monitoring: > - `os::elapsedVTime()` could silently fall back from CPU time to wall time, > according to os_linux.cpp. We'd rather to have true CPU time, or nothing. > Mixing up CPU time and wall time is confusing to users. > - `_vtime_accum` only tracks the time consumed by the concurrent marking main > thread, but not the concurrent worker threads. > > There's a `G1ConcurrentMarkThread::vtime_accum()` that seems to account for > concurrent worker threads. It looks only used for logging. It might be > possible to replace the existing logging code with the value of the > `sun.threads.cpu_time.gc_conc_mark` hsperf counter. However, it is better to > do that separately, and I'll create an RFE. > >> I believe the purpose of calling update_concurrent_mark_threads_cpu_time in >> multiple places is to get more up-to-date conc-cpu-time. Reading through the >> JBS ticket, I don't see the motivation for maintaining such a "fresh" value. > > Yes. The reason is that a concurrent mark cycle could take many seconds or > even minutes for a large heap. For tools like > [AHS](https://mail.openjdk.org/pipermail/hotspot-dev/2022-September/064190.html) > that reads these CPU hsperf counters, they could read these CPU data every 1 > to 5 seconds. > > The current mechanism still needs to wait for the whole > `G1ConcurrentMark::mark_from_roots()` to complete, which could still take > minutes. I can create a separate RFE to make it update more frequently inside > `G1CMConcurrentMarkingTask::work()`.
I've created https://bugs.openjdk.org/browse/JDK-8318937 and https://bugs.openjdk.org/browse/JDK-8318941. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/15082#discussion_r1373893351
