RFR: 8254723: add diagnostic command to write Linux perf map file
Vladimir Sitnikov
github.com+213894+vlsi at openjdk.java.net
Tue Oct 20 11:46:27 UTC 2020
On Tue, 20 Oct 2020 09:27:45 GMT, Nick Gasson <ngasson at 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
test/hotspot/jtreg/serviceability/dcmd/compiler/PerfMapTest.java line 68:
> 66: Matcher m = outputPattern.matcher(line);
> 67:
> 68: Assert.assertTrue(m.matches(), "Did not print map file name");
Suggestion:
Assert.assertTrue(m.matches(), "Did not print map file name, line = " + line);
-------------
PR: https://git.openjdk.java.net/jdk/pull/760
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