basic thread question

[Jan Kaliszewski]

18-08-2009 o 22:10:15 Derek Martin <code at pizzashack.org> wrote:

> I have some simple threaded code...  If I run this
> with an arg of 1 (start one thread), it pegs one cpu, as I would
> expect.  If I run it with an arg of 2 (start 2 threads), it uses both
> CPUs, but utilization of both is less than 50%.  Can anyone explain
> why?
>
> I do not pretend it's impeccable code, and I'm not looking for a
> critiqe of the code per se, excepting the case where what I've written
> is actually *wrong*. I hacked this together in a couple of minutes,
> with the intent of pegging my CPUs.  Performance with two threads is
> actually *worse* than with one, which is highly unintuitive.  I can
> accomplish my goal very easily with bash, but I still want to
> understand what's going on here...
>
> The OS is Linux 2.6.24, on a Ubuntu base.  Here's the code:

Python threads can't benefit from multiple processors (because of GIL,
see: http://docs.python.org/glossary.html#term-global-interpreter-lock).

'multiprocessing' module is what you need:

http://docs.python.org/library/multiprocessing.html

Cheers,
*j

-- 
Jan Kaliszewski (zuo) <zuo at chopin.edu.pl>