[Zope] Re: Give it a rest + answers. (Re: Re: Zope + Apache on Quad Debian machine)

[Tres Seaver]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Dario Lopez-Kästen wrote:

<snip>

> Let me be the first to admit my total lack of knowledge of kernel task
> schedulers, but generally speaking, unless the scheduler makes sure that
> a threaded python process never ever gets distributed over two
> processors simultaniously,  then the GIL *will* be an issue.

The hypothesis is that the scheduler "notices" that threads in a single
Python process are always blocking on a single kernel resource (the
semaphore / mutex which is the GIL), and hence migrates them all to the
same CPU (over time).

I could imagine that this is like the "hand-rolled assembly vs.
compiler-generated code" case:  older kernels (like the one your old app
was dpeloyed atop, perhaps?) didn't have such smarts, but newsr ones do.


> In any event, I'd love to be proved wrong about the need for taskset
> (especially if someone comes up with measurable data to that effect)
> because it means that my sysadmins can simplify their setup for managing
> Zope (making Zope even more acceptable :-).

WHile at ZC, one of the other engineers and I did some testing on SMB
boxes, and found that "one appserver per CPU" gave us near linear
scaling of the application, without any explicit affinity set.  I don't
have the numbers (we were using stock Dell 1U dual CPU boxes, I think),
but the win seemed clear enough that we quit invesigating taskset.


Tres.
- --
===================================================================
Tres Seaver          +1 202-558-7113          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

iD8DBQFEIVAK+gerLs4ltQ4RAnb9AKC7qw38+BqNdAbY79bqPR4/G7USCwCbBmit
UX+GcftjNQ5fUKajALsEbSk=
=+E5c
-----END PGP SIGNATURE-----