Antoine Pitrou <pit...@free.fr> added the comment: > Just use some conversion formula, e.g. switching interval in micro > seconds = constant * byte code check interval. We can then determine > a constant to match todays CPU performance.
Well, there are two problems: - opcode execution cost varies so wildly that trying to pick up an average would be meaningless (it can vary by many order of magnitudes between e.g. a POP_TOP and a CALL_FUNCTION calling a C extension method) - the interval doesn't have the same effect in the new GIL as it has in the old GIL; in the old GIL, it merely gives the OS a chance to switch threads if it wants to (there are many missed opportunities, by a proportion which will be system-dependent); in the new GIL, thread switching is enforced which means it is not necessary to stop so often. So we'd have a formula like: new GIL interval = old GIL interval * opcode duration / proportion of missed switching opportunities in the old GIL where two of the three factors on the right side are totally unpredictable :) > Perhaps I'm missing some feature of the new GIL. Is there some > documentation for it somewhere ? Almost nothing besides what is found in ceval_gil.h and in the following thread: http://mail.python.org/pipermail/python-dev/2009-October/093321.html Dave Beazley did a high-level presentation about it: http://www.dabeaz.com/python/NewGIL.pdf > > Well, if you don't use any threads you don't have to change the setting > > in the first place :-). You might want to do it in order to > > "micro-optimize" your app (i.e. save 1-2% on CPU-bound code), but this > > is unnecessary with the new GIL, since the interval is ignored when > > there's only one thread running. > > Hmm, how do you determine that only one thread is running ? Actually, I don't determine it, it's a side effect of how the GIL is implemented. If no thread is waiting for the GIL, the main thread isn't "asked" to drop it. > What if an extension uses threads that are not under Python > control, e.g. when embedding the JVM or when using a CORBA > ORB ? These don't wait for the GIL, hopefully :-) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue7753> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
