[Cython] Utilities, cython.h, libcython

mark florisson markflorisson88 at gmail.com
Thu Oct 6 11:46:20 CEST 2011

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.

> 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.
> Stefan
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