RFR: 7903722: JMH: Add xctrace-based perfnorm profiler for macOS [v3]

[Aleksey Shipilev]

On Mon, 23 Sep 2024 22:41:01 GMT, Filipp Zhinkin <fzhinkin at openjdk.org> wrote:

>> Implementation of a perfnorm-alike profiler for macOS based on `xctrace` command line tool bundled with Xcode.
>> 
>> While the profiler is tested and seems to be working well, I consider it rather a preliminary version and open to a discussion on what and how it should measure.
>> 
>> Currently, the profiler only supports PMU counters sampling using `CPU Counters` instrument provided by the Instruments app / xctrace.
>> Unfortunately, `CPU Counters` instrument has no default settings, unlike `Time Profiler` and `CPU Profiler` instruments used by the recently merged `xctraceasm` profiler.
>> To use `CPU Counters`, a user has to create a template in the Instruments UI, select PMU events, save the template and then supply to `xctracenorm` as an argument.
>> 
>> This workflow not only prevents use of the profiler without preliminary manual configuration, but also tends to be annoying when it comes to measuring multiple events, as xctrace, unlike perf_events, does not support events multiplexing.
>> 
>> Thankfully, command-line-based configuration and default parameters could be emulated by building a custom Instruments package that imports data from `CPU Counters` and also supplies all required parameters.
>> As you can guess, there's no way to get information about supported PMU events directly from xctrace, but it could be fetched from KPEP database files, stored is `/usr/share/kpep`.
>> `xctracenorm` relies on that data to validate events specified by a user, if any, and also to print a help message that gives some insights into what could be sampled.
>> 
>> To sum up, there are a few things that were implemented to make `xctracenorm` profiler works:
>> - CPU model deletion using `sysctl`;
>> - KPEP file parsing to extract information about the PMU and all supported events;
>> - selected performance events validation;
>> - Instruments package building (generate XML, call a builder tool), packages are cached in `~/Library/Caches/org.openjdk.jmh`;
>> - xctrace execution, resulting samples extraction, and aggregation;
>> - samples postprocessing to calculate some additional metrics, like CPI and branch missprediction ratio.
>> 
>> Currently, if a user didn't specify any additional options, `xctracenorm` will sample instructions, cycles, branches and mispredicted branches events. 
>> These were selected as events that should be supported in all hardware macOS runs on; only 4 events were selected for the same reason.
>> 
>> Profiling results look like this on M2-based MacBook:
>> 
>> j...
>
> Filipp Zhinkin has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - 7903722: Abbreviate units
>  - 7903722: Reuse default template in tests
>  - 7903722: Fixed typos

I think this is good for MVP :)

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Marked as reviewed by shade (Committer).

PR Review: https://git.openjdk.org/jmh/pull/131#pullrequestreview-2326020626