On Wed, 21 Oct 2020 09:13:08 GMT, Nick Gasson <ngas...@openjdk.org> wrote:
>> 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 > > Nick Gasson has updated the pull request incrementally with one additional > commit since the last revision: > > Update for review comments src/hotspot/share/code/codeCache.cpp line 1571: > 1569: if (!fs.is_open()) { > 1570: log_warning(codecache)("Failed to create %s for perf map", fname); > 1571: st->print_cr("Failed to create %s", fname); `st->print_cr()` is still needed? and also I've intended to replace all `print_cr()` to UL (L1587) ------------- PR: https://git.openjdk.java.net/jdk/pull/760
