The testing patch I submitted to the tracker includes a semaphore as well, and I did take some time to try it out. It seems that it's no better than the event object, either for a single thread or scaled to many threads... so this does appear to indicate that the WaitForXX functions are costly (which is expected) and scale terribly (which is unfortunate). I had always believed event objects to be "slower" but I'm not seeing a difference here compared to semaphores. My guess is that these results could be very different if I were to test on, say, Windows 2000 instead of Vista.
- Phillip 2009/5/28 Kristján Valur Jónsson <krist...@ccpgames.com>: > You are right, a small experiment confirmed that it is set to 0 (see > SetCriticalSectionSpinCount()) > I had assumed that a small non-zero value might be chosen on multiprocessor > machines. > > Do you think that the problem lies with the use of the "event" object as > such? Have you tried using a "semaphore" or "mutex" instead? Or do you > think that all of the synchronizations primitives that rely on the > WaitForMultipleObjects() api are subject to the same issue? > > Cheers, > > Kristján > > -----Original Message----- > From: python-dev-bounces+kristjan=ccpgames....@python.org > [mailto:python-dev-bounces+kristjan=ccpgames....@python.org] On Behalf Of > Phillip Sitbon > Sent: 27. maí 2009 22:23 > To: python-dev > Subject: Re: [Python-Dev] Making the GIL faster & lighter on Windows > > > If I'm not mistaken, calling InitializeCriticalSection rather than > InitializeCriticalSectionAndSpinCount (gotta love those long function > names) sets the spin count to zero. I could tell when the spin count > wasn't zero as far as performance is concerned - spinning is too much > of a gamble in most contention situations. > >> I don't know what kernel primitive the Critical Section uses, but if it >> uses an Event object or something similar, we are in the same soup, so to >> say, because the CriticalSection's spinlocking feature buys us nothing. > > Judging from the increase in speed and CPU utilization I've seen, I > don't believe this is the case. My guess is that it's something > similar to a futex. > > > _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
