On Tue, 12 Aug 2025 12:24:35 GMT, Jonas Norlinder <d...@openjdk.org> wrote:
>> Hi all, >> >> This PR refactors the newly added GC CPU time code from >> [JDK-8359110](https://bugs.openjdk.org/browse/JDK-8359110). >> >> As a stepping-stone to enable consolidation of CPU time tracking in e.g. >> hsperf counters and GCTraceCPUTime and to have a unified interface for >> tracking CPU time of various components in Hotspot this code can be >> refactored. This PR introduces a new interface to retrieve CPU time for >> various Hotspot components and it currently supports: >> >> CPUTimeUsage::GC::total() // the sum of gc_threads(), vm_thread(), >> stringdedup() >> >> CPUTimeUsage::GC::gc_threads() >> CPUTimeUsage::GC::vm_thread() >> CPUTimeUsage::GC::stringdedup() >> >> CPUTimeUsage::Runtime::vm_thread() >> >> >> I moved `CPUTimeUsage` to `src/hotspot/share/services` since it seemed >> fitting as it housed similar performance tracking code like >> `RuntimeService`, as this is no longer a class that is only specific to GC. >> >> I also made a minor improvement in the CPU time logging during exit. Since >> `CPUTimeUsage` supports more components than just GC I changed the logging >> flag to from `gc,cpu` to `cpu` and created a detailed table: >> >> >> [71.425s][info][cpu ] === CPU time Statistics >> ============================================================= >> [71.425s][info][cpu ] >> CPUs >> [71.425s][info][cpu ] >> s % utilized >> [71.425s][info][cpu ] Process >> [71.425s][info][cpu ] Total >> 1616.3627 100.00 22.6 >> [71.425s][info][cpu ] VM Thread >> 5.2992 0.33 0.1 >> [71.425s][info][cpu ] Garbage Collection >> 83.7322 5.18 1.2 >> [71.425s][info][cpu ] GC Threads >> 82.7671 5.12 1.2 >> [71.425s][info][cpu ] VM Thread >> 0.9651 0.06 0.0 >> [71.425s][info][cpu ] >> ===================================================================================== >> >> >> Additionally, if CPU time retrieval fails it should not be the caller's >> responsibility to log warnings as this would bloat the code unnecessarily. >> I've noticed that `os` does log a warning for some methods if they fail so I >> continued on this path. > > Jonas Norlinder has updated the pull request incrementally with one > additional commit since the last revision: > > Feedback from Albert Thanks for looking at this and improving the CPU tracking and making it easily accessible. Overall I think the change looks good, just a few comments/questions. src/hotspot/os/linux/os_linux.cpp line 4953: > 4951: // to detach itself from the VM - which should result in ESRCH. > 4952: assert_status(rc == ESRCH, rc, "pthread_getcpuclockid failed"); > 4953: log_warning(os)("Could not sample thread CPU time (return code > %d)", rc); Do we really want add a warning here? This API is used from a lot a places and reading the comment above i sound like it might happen from time to time without it being a very big deal? The risk I see is that we sometimes will get a bunch of these warning in test and they will fail because we can't handle the additional output. The same goes for the other warnings below. src/hotspot/share/gc/shared/collectedHeap.cpp line 655: > 653: print_tracing_info(); > 654: > 655: log_cpu_time(); As mentioned offline, I would prefer if this was moved away from `CollectedHeap` since it is now not only GC/Heap related times that are tracked. We could add a `Universe::before_exit()` which firsts does the CPU logging before calling `heap()->before_exit()`. As long as we do the logging before, would there be any problem with this? ------------- Changes requested by sjohanss (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/26621#pullrequestreview-3119416367 PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2275777432 PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2275805357
