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Co-authored-by: Aniket Panse <aniketpanse@fb.com> Co-authored-by: Gregory P. Smith <greg@krypto.org> Co-authored-by: Carl Meyer <carl@oddbird.net>
51 lines
2.3 KiB
ReStructuredText
51 lines
2.3 KiB
ReStructuredText
.. highlight:: c
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.. _perfmaps:
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Support for Perf Maps
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----------------------
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On supported platforms (as of this writing, only Linux), the runtime can take
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advantage of *perf map files* to make Python functions visible to an external
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profiling tool (such as `perf <https://perf.wiki.kernel.org/index.php/Main_Page>`_).
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A running process may create a file in the ``/tmp`` directory, which contains entries
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that can map a section of executable code to a name. This interface is described in the
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`documentation of the Linux Perf tool <https://git.kernel.org/pub/scm/linux/
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kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jit-interface.txt>`_.
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In Python, these helper APIs can be used by libraries and features that rely
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on generating machine code on the fly.
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Note that holding the Global Interpreter Lock (GIL) is not required for these APIs.
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.. c:function:: int PyUnstable_PerfMapState_Init(void)
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Open the ``/tmp/perf-$pid.map`` file, unless it's already opened, and create
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a lock to ensure thread-safe writes to the file (provided the writes are
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done through :c:func:`PyUnstable_WritePerfMapEntry`). Normally, there's no need
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to call this explicitly; just use :c:func:`PyUnstable_WritePerfMapEntry`
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and it will initialize the state on first call.
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Returns ``0`` on success, ``-1`` on failure to create/open the perf map file,
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or ``-2`` on failure to create a lock. Check ``errno`` for more information
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about the cause of a failure.
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.. c:function:: int PyUnstable_WritePerfMapEntry(const void *code_addr, unsigned int code_size, const char *entry_name)
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Write one single entry to the ``/tmp/perf-$pid.map`` file. This function is
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thread safe. Here is what an example entry looks like::
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# address size name
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7f3529fcf759 b py::bar:/run/t.py
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Will call :c:func:`PyUnstable_PerfMapState_Init` before writing the entry, if
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the perf map file is not already opened. Returns ``0`` on success, or the
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same error codes as :c:func:`PyUnstable_PerfMapState_Init` on failure.
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.. c:function:: void PyUnstable_PerfMapState_Fini(void)
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Close the perf map file opened by :c:func:`PyUnstable_PerfMapState_Init`.
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This is called by the runtime itself during interpreter shut-down. In
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general, there shouldn't be a reason to explicitly call this, except to
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handle specific scenarios such as forking.
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