Development for dual core machine

[Bryan Olson]

Andy wrote:
> I'm going to develop a software package that includes a web server
> (and PHP code) , a database, and some Python code of course.  I am
> being strongly suggested to make it to work on a dual- or multi-core
> computer, but I'm confused on how to take advantage of the multiple
> CPUs.
> 
> From what I read, I think that simply by making the package run in
> several separate processes (web server, database server, Python
> interpreter, etc.), and/or using multiple threads (which I will
> anyway) the package should be able to use multiple CPUs.

Right. There is a theoretical possibility that Python's GIL
could limit thread parallelism, but in this kind of application
it should not matter in the least. Either you're I/O bound, or
there are plenty of tasks the operating system could schedule.

If you have the option to run the Python interpreter within a
web-server process, that's usually a performance winner.

> Is my understanding correct?  So actually, all I have to do is just
> write my multi-threaded Python code as usual?  And how is it decided
> which process and which threads go to CPU 1, CPU 2, etc.?  Perhaps the
> BIOS?

The O.S. actually. A lot of really smart people have put a whole
lot of work into making the O.S. do that well.

If you usually write your Python apps multi-threaded, as I do,
that's fine. Multi-core efficiency has only a little to do with
it. Web service are, for the most part, intrinsically
parallelizable: run multiple web servers, and multiple Python
interpreters serving multiple connections.

The only hard part is shared data. Scalability is all about
the database.


-- 
--Bryan