38 lines
1.9 KiB
Markdown
38 lines
1.9 KiB
Markdown
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# What is this?
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//base/profiler implements a
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[statistical profiler](https://en.wikipedia.org/wiki/Profiling_(computer_programming)#Statistical_profilers)
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for Chrome execution. It supports periodic sampling of thread stacks for the
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purpose of understanding how frequently different parts of the Chrome code are
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being executed. The profiler is used to collect execution information by UMA,
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for broad-scale profiling, and by Chrometto, for targeted profiling during
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tracing.
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## Technical Overview
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The primary entry point to this code is
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[StackSamplingProfiler](stack_sampling_profiler.h). This class regularly
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records the list of currently executing functions on a target thread. See
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the comments above that function for an overview of how to use the profiler.
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The details are very platform-specific, but the major sub-components are
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* A dedicated thread is created to periodically wake up and sample the target
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thread. At each wake up:
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* A [StackCopier](stack_copier.h) copies the target thread's stack
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memory into a [StackBuffer](stack_buffer.h).
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* One or more [Unwinders](unwinder.h) take the memory blob in the StackBuffer
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and turn it into a list of function [Frames](frame.h). Every platform has
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a native unwinder to deal with C++ frames; there are also unwinders for
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V8's special frame layout and for Java frames.
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* Frames have the function instruction address and some module information
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from [ModuleCache](module_cache.h). This should be enough for a program
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with access to the original debug information to reconstruct the names of
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the functions in the stack. The actual conversion back to human-readable
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names is not part of this directory's code.
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* A subclass of [ProfileBuilder](profile_builder.h) is called with a vector
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of Frames corresponding to one stack. The various users of this code are
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responsible for implementing this subclass and recording the stacks in the
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manner they see fit.
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