[Cython] Utilities, cython.h, libcython

Vitja Makarov vitja.makarov at gmail.com
Thu Oct 6 22:56:43 CEST 2011

2011/10/6 mark florisson <markflorisson88 at gmail.com>:
> On 6 October 2011 07:46, Stefan Behnel <stefan_ml at behnel.de> wrote:
>> mark florisson, 05.10.2011 15:53:
>>> On 5 October 2011 08:16, Stefan Behnel wrote:
>>>> mark florisson, 04.10.2011 23:19:
>>>>> Another issue is that Cython compile time is increasing with the
>>>>> addition of control flow and cython utilities. If you use fused types
>>>>> you're also going to combinatorially add more compile time.
>>>> I don't see that locally - a compiled Cython is hugely fast for me. In
>>>> comparison, the C compiler literally takes ages to compile the result. An
>>>> external shared library may or may not help with both - in particular, it
>>>> is
>>>> not clear to me what makes the C compiler slow. If the compile time is
>>>> dominated by the number of inlined functions (which is not unlikely), a
>>>> shared library + header file will not make a difference.
>>> Have you tried with the memoryviews merged?
>> No. I didn't expect the difference to be quite that large.
>>> e.g. if I have this code:
>>> from libc.stdlib cimport malloc
>>> cdef int[:] slice =<int[:10]>  <int *>  malloc(sizeof(int) * 10)
>>> [0] [14:45] ~  ➤ time cython test.pyx
>>> cython test.pyx  2.61s user 0.08s system 99% cpu 2.695 total
>>> [0] [14:45] ~  ➤ time zsh compile
>>> zsh compile  1.88s user 0.06s system 99% cpu 1.946 total
>>> where 'compile' is the script that invoked the same gcc command
>>> distutils uses.  As you can see it took more than 2.5 seconds to
>>> compile this code (simply because the memoryview utilities get
>>> included).
>> Ok, that hints at serious performance problems. Could you profile it to see
>> where the issues are? Is it more that the code is loaded from an external
>> file? Or the fact that more utility code is parsed than necessary?
> I haven't profiled it yet (I'll do that), but I'm fairly sure it's the
> parsing of Cython utility files (not the loading). Maybe Tempita also
> adds to the overhead, I'll find out.

Compiling this regex gives 5ms instead of 10ms on my machine


And on your example gives 3% speedup

>> It's certainly not obvious why the inclusion of static code, even from an
>> external file, should make any difference.
>> That being said, it's not we were lacking the infrastructure for making
>> Python code run faster ...
> Heh, indeed. In this case I think caching will solve all our problems.
>>>>> I'm sure
>>>>> this came up earlier, but I really think we should have a libcython
>>>>> and a cython.h. libcython (a shared library) should contain any common
>>>>> Cython-specific code not meant to be inlined, and cython.h any types,
>>>>> macros and inline functions etc.
>>>> This has a couple of implications though. In order to support this on the
>>>> user side, we have to build one shared library per installed package in
>>>> order to avoid any Cython versioning issues. Just installing a versioned
>>>> "libcython_x.y.z.so" globally isn't enough, especially during
>>>> development,
>>>> but also at deployment time. Different packages may use different CFLAGS
>>>> or
>>>> Cython options, which may have an impact on the result. Encoding all
>>>> possible factors in the file name will be cumbersome and may mean that we
>>>> still end up with a number of installed Cython libraries that correlates
>>>> with the number of installed Cython based packages.
>>> Hm, I think the CFLAGS are important so long as they are compatible
>>> with Python. When the user compiles a Cython extension module with
>>> extra CFLAGS, this doesn't affect libpython. Similarly, the Cython
>>> utilities are really not the user's responsibility, so libcython
>>> doesn't need to be compiled with the same flags as the extension
>>> module. If still wanted, the user could either recompile python with
>>> different CFLAGS (which means libcython will get those as well), or
>>> not use libcython at all. CFLAGS should really only pertain to user
>>> code, not to the Cython library, which the user shouldn't be concerned
>>> about.
>> Well, it's either the user or the OS distribution that installs (and
>> potentially builds) the libraries. That already makes it two responsible
>> entities for many systems that have to agree on what gets installed in what
>> way. I'm just saying, don't underestimate the details in world wide
>> deployments.


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