On Tue, 27 Oct 2020 01:07:04 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> Nick Gasson has updated the pull request with a new target base due to a >> merge or a rebase. The pull request now contains four commits: >> >> - Merge master >> - Add -XX:+DumpPerfMapAtExit option >> - Update for review comments >> - 8254723: add diagnostic command to write Linux perf map file >> >> When using the Linux "perf" tool to do system profiling, symbol names of >> running Java methods cannot be decoded, resulting in unhelpful output >> such as: >> >> 10.52% [JIT] tid 236748 [.] 0x00007f6fdb75d223 >> >> Perf can read a simple text file format describing the mapping between >> address ranges and symbol names for a particular process [1]. >> >> It's possible to generate this already for Java processes using a JVMTI >> plugin such as perf-map-agent [2]. However this requires compiling >> third-party code and then loading the agent into your Java process. It >> would be more convenient if Hotspot could write this file directly using >> a diagnostic command. The information required is almost identical to >> that of the existing Compiler.codelist command. >> >> This patch adds a Compiler.perfmap diagnostic command on Linux only. To >> use, first run "jcmd <pid> Compiler.perfmap" and then "perf top" or >> "perf record" and the report should show decoded Java symbol names for >> that process. >> >> As this just writes a snapshot of the code cache when the command is >> run, it will become stale if methods are compiled later or unloaded. >> However this shouldn't be a big problem in practice if the map file is >> generated after the application has warmed up. >> >> [1] >> https://github.com/torvalds/linux/blob/master/tools/perf/Documentation/jit-interface.txt >> [2] https://github.com/jvm-profiling-tools/perf-map-agent > > Hi Nick, > > This looks good. > Thank you for the update. > > Thanks, > Serguei > I don't see any reason for this to be a product flag, rather than diagnostic. OK sure, I've made it a diagnostic flag. ------------- PR: https://git.openjdk.java.net/jdk/pull/760
