On Tue, 20 Oct 2020 09:27:45 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 Changes requested by ysuenaga (Reviewer). src/hotspot/share/services/diagnosticCommand.hpp line 589: > 587: return "Write map file for Linux perf tool."; > 588: } > 589: static const char* impact() { This operation does not seems to happen in Safepoint. It can be defined as "Low" IMHO. src/hotspot/share/code/codeCache.cpp line 1562: > 1560: } > 1561: > 1562: void CodeCache::write_perf_map(outputStream* st) { Should this code (and changes in header files) be included for Linux only? (`#ifdef LINUX` like the change in diagnosticCommand.cpp) src/hotspot/share/code/codeCache.cpp line 1570: > 1568: fileStream fs(fname, "w"); > 1569: if (!fs.is_open()) { > 1570: st->print_cr("Failed to create %s", fname); This message should be used Unified Logging. ------------- PR: https://git.openjdk.java.net/jdk/pull/760
