[Python-Dev] Re: [Python-checkins] python/nondist/peps pep-0329.txt, 1.2, 1.3

[Jeremy Hylton]

On Wed, 2004-04-21 at 10:50, Phillip J. Eby wrote:
> I could be wrong, but it seems to me that globals shouldn't be nearly as 
> bad for performance as builtins.  A global only does one dict lookup, while 
> builtins do two.  Also, builtins can potentially be optimized away 
> altogether (e.g. 'while True:') or converted to fast LOAD_CONST, or perhaps 
> even a new CALL_BUILTIN opcode, assuming that adding the opcode doesn't 
> blow the cacheability of the eval loop.

The coarse measurements I made a couple of years ago suggest that
LOAD_GLOBAL is still substantially slower than LOAD_FAST.  Less than 100
cycles for LOAD_FAST and about 400 cycles for LOAD_GLOBAL.

http://zope.org/Members/jeremy/CurrentAndFutureProjects/PerformanceMeasurements

It would be good to repeat the measurements with current Python.  I
suspect it's a lot harder to figure out where to measure the start and
stop times.  The timestamps would need to be integrated with PREDICT and
fast_next_opcode, for example.

Jeremy