[Python-Dev] tiny optimization in ceval mainloop

[Guido van Rossum]

> Someone <wink> may wish to question the historical 10 too.  A few weeks ago
> on c.l.py, a number of programs were posted showing that, on Linux, the
> thread scheduling is such the the *offer* to switch threads every 10
> bytecodes was usually declined:  the thread that got the GIL was
> overwhelmingly most often the thread that released it, so that the whole
> dance was overwhelmingly most often pure overhead.  This may be different
> under 2.3, where the pthreads GIL is implemented via a semaphore rather than
> a condvar.  But in that case, actually switching threads every 10 bytecodes
> is an awful lot of thread switching (10 bytecodes don't take as long as they
> used to <wink>).
> 
> I don't know how to pick a good "one size fits all" value, but suspect 10 is
> "clearly too small".  In app after app, people who discover
> sys.setcheckinterval() discover soon after that performance improves if they
> increase it.

Let's try 100 and see how that works.

--Guido van Rossum (home page: http://www.python.org/~guido/)