[Python-Dev] PATCH: Fast globals/builtins lookups for 2.6 (original) (raw)

Steve Holden steve at holdenweb.com
Fri Nov 30 14:52:34 CET 2007

Neil Toronto wrote:

Guido van Rossum wrote:

Hm.

On my Linux box, in the trunk: Before the patch: Pystone(1.1) time for 50000 passes = 1.16 This machine benchmarks at 43103.4 pystones/second After the patch: Pystone(1.1) time for 50000 passes = 1.14 This machine benchmarks at 43859.6 pystones/second That's only about 1.75% faster. But pystone is a lousy benchmark. I'm not aware of any benchmark that isn't. :) Can you humor me and change the PYLONGLONG to Pyssizet in both PyDictObject and PyFastGlobalsObject and see if that helps? It does on one of my test machines. Speaking of which, here's a question for everybody. I was wondering whether 64 bits is necessary. It takes an hour of concerted effort - nothing but "module.d = 1; del module.d" for an hour straight - to overflow a 32-bit version number. Is anybody going to actually get close to doing that in a global namespace? Of course not. And 640k is as much memory as anyone could reasonably need ...

I don't think a malicious user could exploit it. The most they could do is segfault by doing exactly 2**32 entry-invalidating operations and then one get or set. They've got better things to do if they're running code on your machine.

FWIW - and I wouldn't bother with this if I weren't mucking about with dict internals - with a 32-bit version number, I've verified that gcc emits only one extra instruction in dict functions that increment it. It's two for a 64-bit number. The version test in LOADGLOBAL does take a bit more time with 64 bits, though. That's a good local optimization for today's conditions, probably. Who nows whether it will survive the next ten years. And decisions like that have a weird habit of running into pathological cases whose authors curse you when they find out where the problem arose.

regards Steve

Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/

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