Doc/c-api/perfmaps.rst
.. highlight:: c
.. _perfmaps:
On supported platforms (Linux and macOS), the runtime can take
advantage of perf map files to make Python functions visible to an external
profiling tool (such as perf <https://perf.wiki.kernel.org/index.php/Main_Page>_ or
samply <https://github.com/mstange/samply/>). A running process may create a
file in the /tmp directory, which contains entries that can map a section
of executable code to a name. This interface is described in the
documentation of the Linux Perf tool <https://git.kernel.org/pub/scm/linux/ kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jit-interface.txt>.
In Python, these helper APIs can be used by libraries and features that rely on generating machine code on the fly.
Note that holding an :term:attached thread state is not required for these APIs.
.. c:function:: int PyUnstable_PerfMapState_Init(void)
Open the /tmp/perf-$pid.map file, unless it's already opened, and create
a lock to ensure thread-safe writes to the file (provided the writes are
done through :c:func:PyUnstable_WritePerfMapEntry). Normally, there's no need
to call this explicitly; just use :c:func:PyUnstable_WritePerfMapEntry
and it will initialize the state on first call.
Returns 0 on success, -1 on failure to create/open the perf map file,
or -2 on failure to create a lock. Check errno for more information
about the cause of a failure.
.. c:function:: int PyUnstable_WritePerfMapEntry(const void *code_addr, size_t code_size, const char *entry_name)
Write one single entry to the /tmp/perf-$pid.map file. This function is
thread safe. Here is what an example entry looks like::
# address size name
7f3529fcf759 b py::bar:/run/t.py
Will call :c:func:PyUnstable_PerfMapState_Init before writing the entry, if
the perf map file is not already opened. Returns 0 on success, or the
same error codes as :c:func:PyUnstable_PerfMapState_Init on failure.
.. c:function:: void PyUnstable_PerfMapState_Fini(void)
Close the perf map file opened by :c:func:PyUnstable_PerfMapState_Init.
This is called by the runtime itself during interpreter shut-down. In
general, there shouldn't be a reason to explicitly call this, except to
handle specific scenarios such as forking.
.. c:function:: int PyUnstable_CopyPerfMapFile(const char *parent_filename)
Open the /tmp/perf-$pid.map file and append the content of parent_filename
to it.
This function is available on all platforms but only generates output on platforms that support perf maps (currently only Linux). On other platforms, it does nothing.
.. versionadded:: 3.13
.. c:function:: int PyUnstable_PerfTrampoline_CompileCode(PyCodeObject *code)
Compile the given code object using the current perf trampoline.
The "current" trampoline is the one set by the runtime or the most recent
:c:func:PyUnstable_PerfTrampoline_SetPersistAfterFork call.
If no trampoline is set, falls back to normal compilation (no perf map entry).
:param code: The code object to compile. :return: 0 on success, -1 on failure.
.. versionadded:: 3.13
.. c:function:: int PyUnstable_PerfTrampoline_SetPersistAfterFork(int enable)
Set whether the perf trampoline should persist after a fork.
enable is true (non-zero): perf map file remains open/valid post-fork.
Child process inherits all existing perf map entries.enable is false (zero): perf map closes post-fork.
Child process gets empty perf map.Default: false (clears on fork).
:param enable: 1 to enable, 0 to disable. :return: 0 on success, -1 on failure.
.. versionadded:: 3.13