RFR: 7903722: JMH: Add xctrace-based perfnorm profiler for macOS [v2]

[Filipp Zhinkin]

On Sat, 21 Sep 2024 20:56:21 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 16 additional commits since the last revision:
> 
>  - Merge branch 'master' into xctracenorm-prof
>  - 7903722: Use default template instead of generating a package
>  - 7903722: Add extra tests
>  - 7903722: Scan all possible KPEP file locations
>  - 7903722: Serialize xctrace tests execution
>  - 7903722: simplified code, added missing docs, supported branch events
>  - 7903722: Improve events preprocessing
>  - 7903722: Refactor KPEP database loading
>  - 7903722: compute AS Arm64 instructions density metrics
>  - 7903722: check if all listed events could be sampled simultaneously
>  - ... and 6 more: https://git.openjdk.org/jmh/compare/6bd7e794...5a112315

Abbreviated units, not it looks like:

Benchmark                                                          Mode  Cnt   Score   Error      Units
JMHSample_35_Profilers.Atomic.test                                 avgt    5   1.885 ± 0.006      ns/op
JMHSample_35_Profilers.Atomic.test:BRANCH_MISPRED_NONSPEC          avgt       ≈ 10⁻⁵               #/op
JMHSample_35_Profilers.Atomic.test:Branch miss ratio               avgt       ≈ 10⁻⁵           miss/brs
JMHSample_35_Profilers.Atomic.test:CORE_ACTIVE_CYCLE               avgt        6.988               #/op
JMHSample_35_Profilers.Atomic.test:CPI                             avgt        0.584          clks/insn
JMHSample_35_Profilers.Atomic.test:INST_ALL                        avgt       11.970               #/op
JMHSample_35_Profilers.Atomic.test:INST_BRANCH                     avgt        1.995               #/op
JMHSample_35_Profilers.Atomic.test:INST_BRANCH density (of insns)  avgt        0.167             #/insn
JMHSample_35_Profilers.Atomic.test:IPC                             avgt        1.713          insns/clk

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PR Comment: https://git.openjdk.org/jmh/pull/131#issuecomment-2369661435