[Cython] Cython 0.15rc2 and parallelization issue

[Francesc Alted]

Sure.  And I'm seeing a good speed-up on my 2-core machine indeed:

Without parallel loop:

real    0m0.923s
user    0m0.875s
sys     0m0.045s

With parallel loop:

real    0m0.544s
user    0m0.876s
sys     0m0.045s

Which is pretty awesome, given the simplicity of Cython parallel
implementation :)

Thanks a lot Mark!


2011/8/3, mark florisson <markflorisson88 at gmail.com>:
> On 3 August 2011 14:18, Francesc Alted <faltet at pytables.org> wrote:
>> Hi,
>>
>> I'm trying to take advantage of the exciting new parallelizing
>> capabilities recently introduced in forthcoming 0.15 version, but I'm
>> having a small difficulty.  When I try to compile a small demo routing
>> (attached), I'm getting this error:
>>
>> $ cython -a mandel.pyx
>>
>> Error compiling Cython file:
>> ------------------------------------------------------------
>> ...
>>    for pix in prange(num_pixels, nogil=True, schedule="dynamic"):
>>        x = pix % width
>>        y = pix // width
>>        cr = begin_r + (x * span_r / (width + 1.0))
>>        ci = begin_i + (y * span_i / (height + 1.0))
>>        n = MandelbrotCalculate(cr, ci, maxiter)
>>                              ^
>> ------------------------------------------------------------
>>
>> mandel.pyx:50:31: Calling gil-requiring function not allowed without gil
>>
>> While trying to figure out why MandelbrotCalculate does require GIL, I
>> replaced the "for  prange", by a trivial "for range", and the
>> annotated HTML source reveals that the only line in (light) yellow in
>> this function is
>>
>>    return n
>>
>> which is translated as:
>>
>>  /* "mandel.pyx":22
>>  *         ti = 2*zr*zi + ci
>>  *         zr, zi = tr, ti
>>  *     return n             # <<<<<<<<<<<<<<
>>  *
>>  * @cython.boundscheck(False)
>>  */
>>  __pyx_r = __pyx_v_n;
>>  goto __pyx_L0;
>>
>>  __pyx_r = 0;
>>  __pyx_L0:;
>>  __Pyx_RefNannyFinishContext();
>>  return __pyx_r;
>> }
>>
>> My guess is that this __Pyx_RefNannyFinishContext() call is preventing
>> to call the routing from the parallel loop.  Is that a bug, a
>> limitation of current implementation or it is just that I'm missing
>> something?
>>
>> Thanks,
>>
>> --
>> Francesc Alted
>>
>> _______________________________________________
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>> cython-devel at python.org
>> http://mail.python.org/mailman/listinfo/cython-devel
>>
>>
>
> Hey Francesc!
>
> The problem is that you didn't declare MandelbrotCalculate 'nogil'.
> You have to write
>
>     cdef long MandelbrotCalculate(double cr, double ci, long maxiter) nogil:
>         ...
>
> That's all, and it will compile :)
>
> Cheers,
>
> Mark
> _______________________________________________
> cython-devel mailing list
> cython-devel at python.org
> http://mail.python.org/mailman/listinfo/cython-devel
>


-- 
Francesc Alted