Yichun Zhang (agentz - [PATCH] [python] Optimize python_string_to_host_string() for Python 2. (original) (raw)

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• From: "Yichun Zhang (agentzh)"
• To: gdb-patches
• Cc: "Yichun Zhang (agentzh)"
• Date: Tue, 13 Jan 2015 22:38:01 -0800
• Subject: [PATCH] [python] Optimize python_string_to_host_string() for Python 2.
• Authentication-results: sourceware.org; auth=none

Hi,

I have been writing quite some advanced GDB Python tools for LuaJIT and NGINX in the nginx-gdb-utils project [1] and have been suffering from serious performance issues even for relatively small working sets.

I have noticed from a typical on-CPU C-land Flame Graph [2] for my tools that python_string_to_host_string() is painfully slow when using Python 2 (2.7 to be more specific) due to the expensive and meaningless unicode conversions there (involved with hot function calls like utf_8_decode).

With the following patch, my most complicated Python tools finally have comparable performance between Python 2 and Python 3. In the case of Python 2, some real-world Python scripts' overall speedup can be as big as 34% (for my "lgcpath" command [3]) or even 57% (for my "lgcstat" command [4]). And from the new Flame Graph [5], we can see that the corresponding function frames are indeed gone.

Comments are welcome!

[1] https://github.com/openresty/nginx-gdb-utils#readme [2] http://agentzh.org/misc/flamegraph/gdb-py-lgcstat-2015-0113.svg [3] https://github.com/openresty/nginx-gdb-utils#lgcpath [4] https://github.com/openresty/nginx-gdb-utils#lgcstat [5] http://agentzh.org/misc/flamegraph/patched-gdb-py-lgcstat-2015-0113.svg

gdb/ChangeLog:

* python/py-utils.c (python_string_to_host_string): use
xstrdup directly for Python 2.
* python/py-utils.c (gdbpy_obj_to_string): use
python_string_to_host_string for both Python 2 and 3.

gdb/python/py-utils.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/gdb/python/py-utils.c b/gdb/python/py-utils.c index 58a5934..ed7be3b 100644 --- a/gdb/python/py-utils.c +++ b/gdb/python/py-utils.c @@ -209,6 +209,7 @@ python_string_to_target_python_string (PyObject *obj) char * python_string_to_host_string (PyObject *obj) { +#ifdef IS_PY3K PyObject *str; char *result; @@ -219,6 +220,9 @@ python_string_to_host_string (PyObject obj) result = unicode_to_encoded_string (str, host_charset ()); Py_DECREF (str); return result; +#else + return xstrdup (PyString_AsString (obj)); +#endif } / Return true if OBJ is a Python string or unicode object, false @@ -245,12 +249,7 @@ gdbpy_obj_to_string (PyObject *obj) if (str_obj != NULL) { -#ifdef IS_PY3K char *msg = python_string_to_host_string (str_obj); -#else - char *msg = xstrdup (PyString_AsString (str_obj)); -#endif

   Py_DECREF (str_obj);
   return msg;
 }

-- 1.8.5.6

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    * From: Yichun Zhang (agentzh)