[Python-Dev] cpython (2.7): Fix comment blocks. Adjust blocksize to a power-of-two for better divmod

[Benjamin Peterson]

I've backed this one out, too.

2013/6/22 Scott Dial <scott+python-dev at scottdial.com>:
> On 6/22/2013 2:17 PM, Benjamin Peterson wrote:
>> Many people have raised concerns about this change, so I've now backed it out.
>
> I think that change also goes with this change:
>
> http://hg.python.org/cpython/rev/f1dc30a1be72
>
> changeset 84248:f1dc30a1be72 2.7
> Arrange structure to match the common access patterns.
>
>      1.1 --- a/Modules/_collectionsmodule.c
>      1.2 +++ b/Modules/_collectionsmodule.c
>      1.3 @@ -48,8 +48,8 @@
>      1.4
>      1.5  typedef struct BLOCK {
>      1.6      struct BLOCK *leftlink;
>      1.7 +    PyObject *data[BLOCKLEN];
>      1.8      struct BLOCK *rightlink;
>      1.9 -    PyObject *data[BLOCKLEN];
>     1.10  } block;
>     1.11
>     1.12  #define MAXFREEBLOCKS 10
>
> , which seems like a strange micro-optimization, at best.
>
> Based on that structure, it would seem that neither BLOCKLEN being 62
> (previous value) nor 64 (the new value) make much sense. It would seem
> best that sizeof(block) == 64, so BLOCKLEN should be (64 -
> 2*sizeof(PyObject *)). Nevertheless, I am skeptical that any tuning of
> this structure provides any meaningful performance improvement.
>
> --
> Scott Dial
> scott at scottdial.com



-- 
Regards,
Benjamin