Integrated: 8254723: add diagnostic command to write Linux perf map file

[Nick Gasson]

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

This pull request has now been integrated.

Changeset: 50357d13
Author:    Nick Gasson <ngasson at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/50357d13
Stats:     171 lines in 8 files changed: 169 ins; 1 del; 1 mod

8254723: add diagnostic command to write Linux perf map file

Reviewed-by: ysuenaga, sspitsyn

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PR: https://git.openjdk.java.net/jdk/pull/760