[Python-Dev] Python 3.5 on VC14 (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Wed Jun 11 00:24:48 CEST 2014

Am 10.06.14 18:30, schrieb Steve Dower:

I ran a quick test with profile-guided optimization (PGO, pronounced "pogo"), which has supposedly been improved since VC9, and saw a very unscientific 20% speed improvement on pybench.py and 10% size reduction in python35.dll. I'm not sure what we used to get from VC9, but it certainly seems worth enabling provided it doesn't break anything. (Interestingly, PGO decided that only 1% of functions needed to be compiled for speed. Not sure if I can find out which ones those are but if anyone's interested I can give it a shot?)

You probably ran too little Python code. See PCbuild/build_pgo.bat for what used to be part of the release process. It takes quite some time, but it rebuilt more than 1% (IIRC).

FWIW, I stopped using PGO for the official releases when it was demonstrated to generate bad code. In my experience, a compiler that generates bad code has lost trust "forever", so it will be hard to justify re-enabling PGO (like "but it really works this time"). I wasn't sad when I found a justification to skip the profiling, since it significantly held up the release process.

Regards, Martin

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