mirror of
https://github.com/python/cpython.git
synced 2025-10-31 10:26:02 +00:00
3440d197a5
Discussion: https://discuss.python.org/t/slight-grammar-fix-throughout-adverbs-dont-need-hyphen/17021
436 lines
15 KiB
ReStructuredText
436 lines
15 KiB
ReStructuredText
.. highlight:: shell-session
|
|
|
|
.. _instrumentation:
|
|
|
|
===============================================
|
|
Instrumenting CPython with DTrace and SystemTap
|
|
===============================================
|
|
|
|
:author: David Malcolm
|
|
:author: Łukasz Langa
|
|
|
|
DTrace and SystemTap are monitoring tools, each providing a way to inspect
|
|
what the processes on a computer system are doing. They both use
|
|
domain-specific languages allowing a user to write scripts which:
|
|
|
|
- filter which processes are to be observed
|
|
- gather data from the processes of interest
|
|
- generate reports on the data
|
|
|
|
As of Python 3.6, CPython can be built with embedded "markers", also
|
|
known as "probes", that can be observed by a DTrace or SystemTap script,
|
|
making it easier to monitor what the CPython processes on a system are
|
|
doing.
|
|
|
|
.. impl-detail::
|
|
|
|
DTrace markers are implementation details of the CPython interpreter.
|
|
No guarantees are made about probe compatibility between versions of
|
|
CPython. DTrace scripts can stop working or work incorrectly without
|
|
warning when changing CPython versions.
|
|
|
|
|
|
Enabling the static markers
|
|
---------------------------
|
|
|
|
macOS comes with built-in support for DTrace. On Linux, in order to
|
|
build CPython with the embedded markers for SystemTap, the SystemTap
|
|
development tools must be installed.
|
|
|
|
On a Linux machine, this can be done via::
|
|
|
|
$ yum install systemtap-sdt-devel
|
|
|
|
or::
|
|
|
|
$ sudo apt-get install systemtap-sdt-dev
|
|
|
|
|
|
CPython must then be :option:`configured with the --with-dtrace option
|
|
<--with-dtrace>`:
|
|
|
|
.. code-block:: none
|
|
|
|
checking for --with-dtrace... yes
|
|
|
|
On macOS, you can list available DTrace probes by running a Python
|
|
process in the background and listing all probes made available by the
|
|
Python provider::
|
|
|
|
$ python3.6 -q &
|
|
$ sudo dtrace -l -P python$! # or: dtrace -l -m python3.6
|
|
|
|
ID PROVIDER MODULE FUNCTION NAME
|
|
29564 python18035 python3.6 _PyEval_EvalFrameDefault function-entry
|
|
29565 python18035 python3.6 dtrace_function_entry function-entry
|
|
29566 python18035 python3.6 _PyEval_EvalFrameDefault function-return
|
|
29567 python18035 python3.6 dtrace_function_return function-return
|
|
29568 python18035 python3.6 collect gc-done
|
|
29569 python18035 python3.6 collect gc-start
|
|
29570 python18035 python3.6 _PyEval_EvalFrameDefault line
|
|
29571 python18035 python3.6 maybe_dtrace_line line
|
|
|
|
On Linux, you can verify if the SystemTap static markers are present in
|
|
the built binary by seeing if it contains a ".note.stapsdt" section.
|
|
|
|
::
|
|
|
|
$ readelf -S ./python | grep .note.stapsdt
|
|
[30] .note.stapsdt NOTE 0000000000000000 00308d78
|
|
|
|
If you've built Python as a shared library
|
|
(with the :option:`--enable-shared` configure option), you
|
|
need to look instead within the shared library. For example::
|
|
|
|
$ readelf -S libpython3.3dm.so.1.0 | grep .note.stapsdt
|
|
[29] .note.stapsdt NOTE 0000000000000000 00365b68
|
|
|
|
Sufficiently modern readelf can print the metadata::
|
|
|
|
$ readelf -n ./python
|
|
|
|
Displaying notes found at file offset 0x00000254 with length 0x00000020:
|
|
Owner Data size Description
|
|
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
|
|
OS: Linux, ABI: 2.6.32
|
|
|
|
Displaying notes found at file offset 0x00000274 with length 0x00000024:
|
|
Owner Data size Description
|
|
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
|
|
Build ID: df924a2b08a7e89f6e11251d4602022977af2670
|
|
|
|
Displaying notes found at file offset 0x002d6c30 with length 0x00000144:
|
|
Owner Data size Description
|
|
stapsdt 0x00000031 NT_STAPSDT (SystemTap probe descriptors)
|
|
Provider: python
|
|
Name: gc__start
|
|
Location: 0x00000000004371c3, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf6
|
|
Arguments: -4@%ebx
|
|
stapsdt 0x00000030 NT_STAPSDT (SystemTap probe descriptors)
|
|
Provider: python
|
|
Name: gc__done
|
|
Location: 0x00000000004374e1, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf8
|
|
Arguments: -8@%rax
|
|
stapsdt 0x00000045 NT_STAPSDT (SystemTap probe descriptors)
|
|
Provider: python
|
|
Name: function__entry
|
|
Location: 0x000000000053db6c, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6be8
|
|
Arguments: 8@%rbp 8@%r12 -4@%eax
|
|
stapsdt 0x00000046 NT_STAPSDT (SystemTap probe descriptors)
|
|
Provider: python
|
|
Name: function__return
|
|
Location: 0x000000000053dba8, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bea
|
|
Arguments: 8@%rbp 8@%r12 -4@%eax
|
|
|
|
The above metadata contains information for SystemTap describing how it
|
|
can patch strategically placed machine code instructions to enable the
|
|
tracing hooks used by a SystemTap script.
|
|
|
|
|
|
Static DTrace probes
|
|
--------------------
|
|
|
|
The following example DTrace script can be used to show the call/return
|
|
hierarchy of a Python script, only tracing within the invocation of
|
|
a function called "start". In other words, import-time function
|
|
invocations are not going to be listed:
|
|
|
|
.. code-block:: none
|
|
|
|
self int indent;
|
|
|
|
python$target:::function-entry
|
|
/copyinstr(arg1) == "start"/
|
|
{
|
|
self->trace = 1;
|
|
}
|
|
|
|
python$target:::function-entry
|
|
/self->trace/
|
|
{
|
|
printf("%d\t%*s:", timestamp, 15, probename);
|
|
printf("%*s", self->indent, "");
|
|
printf("%s:%s:%d\n", basename(copyinstr(arg0)), copyinstr(arg1), arg2);
|
|
self->indent++;
|
|
}
|
|
|
|
python$target:::function-return
|
|
/self->trace/
|
|
{
|
|
self->indent--;
|
|
printf("%d\t%*s:", timestamp, 15, probename);
|
|
printf("%*s", self->indent, "");
|
|
printf("%s:%s:%d\n", basename(copyinstr(arg0)), copyinstr(arg1), arg2);
|
|
}
|
|
|
|
python$target:::function-return
|
|
/copyinstr(arg1) == "start"/
|
|
{
|
|
self->trace = 0;
|
|
}
|
|
|
|
It can be invoked like this::
|
|
|
|
$ sudo dtrace -q -s call_stack.d -c "python3.6 script.py"
|
|
|
|
The output looks like this:
|
|
|
|
.. code-block:: none
|
|
|
|
156641360502280 function-entry:call_stack.py:start:23
|
|
156641360518804 function-entry: call_stack.py:function_1:1
|
|
156641360532797 function-entry: call_stack.py:function_3:9
|
|
156641360546807 function-return: call_stack.py:function_3:10
|
|
156641360563367 function-return: call_stack.py:function_1:2
|
|
156641360578365 function-entry: call_stack.py:function_2:5
|
|
156641360591757 function-entry: call_stack.py:function_1:1
|
|
156641360605556 function-entry: call_stack.py:function_3:9
|
|
156641360617482 function-return: call_stack.py:function_3:10
|
|
156641360629814 function-return: call_stack.py:function_1:2
|
|
156641360642285 function-return: call_stack.py:function_2:6
|
|
156641360656770 function-entry: call_stack.py:function_3:9
|
|
156641360669707 function-return: call_stack.py:function_3:10
|
|
156641360687853 function-entry: call_stack.py:function_4:13
|
|
156641360700719 function-return: call_stack.py:function_4:14
|
|
156641360719640 function-entry: call_stack.py:function_5:18
|
|
156641360732567 function-return: call_stack.py:function_5:21
|
|
156641360747370 function-return:call_stack.py:start:28
|
|
|
|
|
|
Static SystemTap markers
|
|
------------------------
|
|
|
|
The low-level way to use the SystemTap integration is to use the static
|
|
markers directly. This requires you to explicitly state the binary file
|
|
containing them.
|
|
|
|
For example, this SystemTap script can be used to show the call/return
|
|
hierarchy of a Python script:
|
|
|
|
.. code-block:: none
|
|
|
|
probe process("python").mark("function__entry") {
|
|
filename = user_string($arg1);
|
|
funcname = user_string($arg2);
|
|
lineno = $arg3;
|
|
|
|
printf("%s => %s in %s:%d\\n",
|
|
thread_indent(1), funcname, filename, lineno);
|
|
}
|
|
|
|
probe process("python").mark("function__return") {
|
|
filename = user_string($arg1);
|
|
funcname = user_string($arg2);
|
|
lineno = $arg3;
|
|
|
|
printf("%s <= %s in %s:%d\\n",
|
|
thread_indent(-1), funcname, filename, lineno);
|
|
}
|
|
|
|
It can be invoked like this::
|
|
|
|
$ stap \
|
|
show-call-hierarchy.stp \
|
|
-c "./python test.py"
|
|
|
|
The output looks like this:
|
|
|
|
.. code-block:: none
|
|
|
|
11408 python(8274): => __contains__ in Lib/_abcoll.py:362
|
|
11414 python(8274): => __getitem__ in Lib/os.py:425
|
|
11418 python(8274): => encode in Lib/os.py:490
|
|
11424 python(8274): <= encode in Lib/os.py:493
|
|
11428 python(8274): <= __getitem__ in Lib/os.py:426
|
|
11433 python(8274): <= __contains__ in Lib/_abcoll.py:366
|
|
|
|
where the columns are:
|
|
|
|
- time in microseconds since start of script
|
|
|
|
- name of executable
|
|
|
|
- PID of process
|
|
|
|
and the remainder indicates the call/return hierarchy as the script executes.
|
|
|
|
For a :option:`--enable-shared` build of CPython, the markers are contained within the
|
|
libpython shared library, and the probe's dotted path needs to reflect this. For
|
|
example, this line from the above example:
|
|
|
|
.. code-block:: none
|
|
|
|
probe process("python").mark("function__entry") {
|
|
|
|
should instead read:
|
|
|
|
.. code-block:: none
|
|
|
|
probe process("python").library("libpython3.6dm.so.1.0").mark("function__entry") {
|
|
|
|
(assuming a :ref:`debug build <debug-build>` of CPython 3.6)
|
|
|
|
|
|
Available static markers
|
|
------------------------
|
|
|
|
.. object:: function__entry(str filename, str funcname, int lineno)
|
|
|
|
This marker indicates that execution of a Python function has begun.
|
|
It is only triggered for pure-Python (bytecode) functions.
|
|
|
|
The filename, function name, and line number are provided back to the
|
|
tracing script as positional arguments, which must be accessed using
|
|
``$arg1``, ``$arg2``, ``$arg3``:
|
|
|
|
* ``$arg1`` : ``(const char *)`` filename, accessible using ``user_string($arg1)``
|
|
|
|
* ``$arg2`` : ``(const char *)`` function name, accessible using
|
|
``user_string($arg2)``
|
|
|
|
* ``$arg3`` : ``int`` line number
|
|
|
|
.. object:: function__return(str filename, str funcname, int lineno)
|
|
|
|
This marker is the converse of :c:func:`function__entry`, and indicates that
|
|
execution of a Python function has ended (either via ``return``, or via an
|
|
exception). It is only triggered for pure-Python (bytecode) functions.
|
|
|
|
The arguments are the same as for :c:func:`function__entry`
|
|
|
|
.. object:: line(str filename, str funcname, int lineno)
|
|
|
|
This marker indicates a Python line is about to be executed. It is
|
|
the equivalent of line-by-line tracing with a Python profiler. It is
|
|
not triggered within C functions.
|
|
|
|
The arguments are the same as for :c:func:`function__entry`.
|
|
|
|
.. object:: gc__start(int generation)
|
|
|
|
Fires when the Python interpreter starts a garbage collection cycle.
|
|
``arg0`` is the generation to scan, like :func:`gc.collect()`.
|
|
|
|
.. object:: gc__done(long collected)
|
|
|
|
Fires when the Python interpreter finishes a garbage collection
|
|
cycle. ``arg0`` is the number of collected objects.
|
|
|
|
.. object:: import__find__load__start(str modulename)
|
|
|
|
Fires before :mod:`importlib` attempts to find and load the module.
|
|
``arg0`` is the module name.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
.. object:: import__find__load__done(str modulename, int found)
|
|
|
|
Fires after :mod:`importlib`'s find_and_load function is called.
|
|
``arg0`` is the module name, ``arg1`` indicates if module was
|
|
successfully loaded.
|
|
|
|
.. versionadded:: 3.7
|
|
|
|
|
|
.. object:: audit(str event, void *tuple)
|
|
|
|
Fires when :func:`sys.audit` or :c:func:`PySys_Audit` is called.
|
|
``arg0`` is the event name as C string, ``arg1`` is a :c:type:`PyObject`
|
|
pointer to a tuple object.
|
|
|
|
.. versionadded:: 3.8
|
|
|
|
|
|
SystemTap Tapsets
|
|
-----------------
|
|
|
|
The higher-level way to use the SystemTap integration is to use a "tapset":
|
|
SystemTap's equivalent of a library, which hides some of the lower-level
|
|
details of the static markers.
|
|
|
|
Here is a tapset file, based on a non-shared build of CPython:
|
|
|
|
.. code-block:: none
|
|
|
|
/*
|
|
Provide a higher-level wrapping around the function__entry and
|
|
function__return markers:
|
|
\*/
|
|
probe python.function.entry = process("python").mark("function__entry")
|
|
{
|
|
filename = user_string($arg1);
|
|
funcname = user_string($arg2);
|
|
lineno = $arg3;
|
|
frameptr = $arg4
|
|
}
|
|
probe python.function.return = process("python").mark("function__return")
|
|
{
|
|
filename = user_string($arg1);
|
|
funcname = user_string($arg2);
|
|
lineno = $arg3;
|
|
frameptr = $arg4
|
|
}
|
|
|
|
If this file is installed in SystemTap's tapset directory (e.g.
|
|
``/usr/share/systemtap/tapset``), then these additional probepoints become
|
|
available:
|
|
|
|
.. object:: python.function.entry(str filename, str funcname, int lineno, frameptr)
|
|
|
|
This probe point indicates that execution of a Python function has begun.
|
|
It is only triggered for pure-Python (bytecode) functions.
|
|
|
|
.. object:: python.function.return(str filename, str funcname, int lineno, frameptr)
|
|
|
|
This probe point is the converse of ``python.function.return``, and
|
|
indicates that execution of a Python function has ended (either via
|
|
``return``, or via an exception). It is only triggered for pure-Python
|
|
(bytecode) functions.
|
|
|
|
|
|
Examples
|
|
--------
|
|
This SystemTap script uses the tapset above to more cleanly implement the
|
|
example given above of tracing the Python function-call hierarchy, without
|
|
needing to directly name the static markers:
|
|
|
|
.. code-block:: none
|
|
|
|
probe python.function.entry
|
|
{
|
|
printf("%s => %s in %s:%d\n",
|
|
thread_indent(1), funcname, filename, lineno);
|
|
}
|
|
|
|
probe python.function.return
|
|
{
|
|
printf("%s <= %s in %s:%d\n",
|
|
thread_indent(-1), funcname, filename, lineno);
|
|
}
|
|
|
|
|
|
The following script uses the tapset above to provide a top-like view of all
|
|
running CPython code, showing the top 20 most frequently entered bytecode
|
|
frames, each second, across the whole system:
|
|
|
|
.. code-block:: none
|
|
|
|
global fn_calls;
|
|
|
|
probe python.function.entry
|
|
{
|
|
fn_calls[pid(), filename, funcname, lineno] += 1;
|
|
}
|
|
|
|
probe timer.ms(1000) {
|
|
printf("\033[2J\033[1;1H") /* clear screen \*/
|
|
printf("%6s %80s %6s %30s %6s\n",
|
|
"PID", "FILENAME", "LINE", "FUNCTION", "CALLS")
|
|
foreach ([pid, filename, funcname, lineno] in fn_calls- limit 20) {
|
|
printf("%6d %80s %6d %30s %6d\n",
|
|
pid, filename, lineno, funcname,
|
|
fn_calls[pid, filename, funcname, lineno]);
|
|
}
|
|
delete fn_calls;
|
|
}
|
|
|