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

[Scott Dial]

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