Re: Hello

["Stephen P. Ryan" <sryan@emmy.dartmouth.edu>]

On 16 Feb, Ben Pfaff wrote in response to someone else who wrote:
>    I would like to know how debian handles in a machine with two pentiums. =
>    Are two cpus quicker then one in any situation. I mean does every =
>    program run quicker.
> 
> Generally any particular process will only run on one processor at a
> time, so particular programs won't run faster.  However, two programs
> can run simultaneously each with a whole processor to themselves, in
> theory anyway.  
> 
> Anyone with any experience in this want to comment?
> 

There are ups and downs to the SMP support in Linux; I have even heard
of situations where running two large memory-intensive applications at
the same time ran slower than one-at-a-time on a single processor
machine.  That said, though, I find that the X server runs on one
processor, and the application runs on another, leading to a *very*
responsive system.  You can have an application computing at full speed
on one processor, while the screen is being updated and you are
movinng windows around etc. on the other processor.

Multi-threaded applications run faster, of course, because they get
more CPU time; several single-threaded applications running
simultaneously depends on the applications and whether they are
compute-bound or I/O bound.  If the applications are I/O bound, then no
amount of extra CPU power will speed them up.  If your applications are
CPU-bound, then you should get nearly twice the performance from having
 two CPUs installed. If you are running only one application at a time
then the only gain you will see comes from having the background
daemons and the X server running on a different CPU from the one
running your application, and I think you'd be better off just getting
a faster video card or more RAM or a faster drive or just about
anything else.

Be warned - the extra speed is addictive.  The only reason I'm giving up
my dual PPro 200 is to get a faster multi-cpu system. 
-- 
Stephen Ryan                   Debian GNU/Linux
Mathematics graduate student, Dartmouth College


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