1. 25 Mar, 2019 1 commit
    • Benedikt Meurer's avatar
      [tracing] Improve tracing signals for compilation/optimization. · a2af7e11
      Benedikt Meurer authored
      This adds OBJECT/SNAPSHOT trace events for Script and SharedFunctionInfo
      objects, logging their creation with appropriate information to make
      sense of them.
      
      Based on that we introduces five flow events to model the optimized
      compilation via tracing in the "disabled-by-default-v8.compile" category:
      
        - "v8.optimizingCompile.start" logs the creation of the
          PipelineCompilationJob (for TurboFan JavaScript optimization)
          with the "function" argument referring to the trace event
          object created for the SharedFunctionInfo.
        - "v8.optimzingCompile.prepare" logs the preparation of the
          PipelineCompilationJob on the main thread, also carrying the
          "function" argument. This connects the flow event to the actual
          tracing duration event associated with the preparation phases.
        - "v8.optimizingCompile.execute" logs the (usually concurrent)
          optimization of the TurboFan graph (again with "function").
        - "v8.optimizingCompile.finalize" logs the main thread phase which
          finalizes the optimized code and eventually installs it (in case
          of success).
        - "v8.optimizingCompile.end" signals the end of the
          PipelineCompilationJob, which carries the "compilationInfo",
          that contains the interesting bits of the OptimizedCompilationInfo,
          specifically whether the compile was successfull and which functions
          were inlined for example.
      
      This also adds two instant events "V8.AbortOptimization" and
      "V8.RetryOptimization" in "disabled-by-default-v8.compile" category
      that are emitted when TurboFan cannot optimize a certain function.
      In case of "V8.RetryOptimization", TurboFan might be able to optimize
      it later, whereas "V8.AbortOptimization" permanently disables the
      optimization of a given function. The JSON representation of this is
      
      ```js
      {
        "pid": 256639,
        "tid": 256639,
        "ts": 6935411377801,
        "tts": 159116,
        "ph": "I",
        "cat": "disabled-by-default-v8.compile",
        "name": "V8.AbortOptimization",
        "dur": 0,
        "tdur": 0,
        "args": {
          "reason": "Function is too big to be optimized",
          "function": {
            "id_ref": "0x600000001",
            "scope": "v8::internal::SharedFunctionInfo"
          }
        }
      },
      ```
      
      where the "function" refers to a previously emitted SNAPSHOT for the
      function in question. In the trace viewer it will show up as instant
      event under "v8.optimizingCompile.prepare" in case of the relevant
      example where optimization is disabled due to reaching the bytecode
      limit (as in the JSON above), i.e. it'll look something like this
      
        https://i.paste.pics/aafc2de9df10ea8f5acc1a761d80f07b.png
      
      for the example highlighted in the recent blog post
      
        https://ponyfoo.com/articles/javascript-performance-pitfalls-v8
      
      that describes the optimization limit. The "v8.optimizingCompile.end"
      duration event will also carry this information as part of the
      "compilationInfo" object, but specifically for CI tools, etc. it might
      be a whole lot easier to just look for the "V8.AbortOptimization"
      instant event.
      
      Bug: v8:8598, v8:9039
      Tbr: ulan@chromium.org
      Doc: bit.ly/v8-tracing-signals
      Change-Id: Ic87ac336004690c65b6b15ad73bc6fbd4b5f12c4
      Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1511483
      Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
      Reviewed-by: 's avatarPeter Marshall <petermarshall@chromium.org>
      Reviewed-by: 's avatarBenedikt Meurer <bmeurer@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#60448}
      a2af7e11
  2. 31 Oct, 2018 1 commit
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