RFR: 8254723: add diagnostic command to write Linux perf map file [v4]

[Serguei Spitsyn]

On Mon, 26 Oct 2020 06:06:47 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
>
> 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

-------------

Marked as reviewed by sspitsyn (Reviewer).

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