News Group Posts

linux multitasking cpu

From: Floyd Davidson <floyd@ptialaska.net>
Subject: Re: Linux multitasking
Date: 29 Mar 2002 12:28:21 -0900
References: <3CA4927A.5050700@sandia.gov> 

"Christopher R. Carlen" <crcarle@sandia.gov> wrote:
>Hi:
>
>I would like to understand why I experience certain kinds of behavior 
>using Linux.  I have Suse 7.3 with 2.4.10.

>I find that it is possible running programs in X, particularly Netscape, 
>that the program can get stuck.  When it does this, the pointer will not 
>  operate on X.  That is, if I try to move out of Netscape's window I 
>can do so, but then no other applications respond either.  The KDE panel 
>doesn't respond.  Nothing.  Not until Netscape recovers, or I kill it by 
>going to a console (the keyboard fortunately responds).

    [big snip]

Richard Pitt provided a rather detailed look at what Linux does
and how the behavior you see happens.

But I think it may have masked some practical answers on what to
do about it.

I can't be sure if your system really is cpu bound, or if it is
just simply being forced into paging by a lack of RAM.  Either
one could cause what you describe, and in particular Netscape
and KDE are both resource hogs that lead to either or both
problems.

Netscape in particular has a bug that occasionally causes it to
just suck up all the available virtual memory a system has.  But
regardless, if your system doesn't have enough RAM it will be
paging things out to swap space.  Of course, if you run out of
swap space too, then things *really* look wedged!

The most obvious solution, is to run xsysinfo or xosview and
watch what is going on when your box emulates a glacier.  If it
needs more RAM or more swap, you won't have to guess.

But in the long run there is one other way to help avoid this
too.  Dual processor motherboards, and relatively inexpensive
cpu's to go in them, are commonly available.  Two cpu's at some
given speed simply will not run single threaded programs at
twice the speed of a single cpu... but, while wedging one cpu
may be common, wedging two isn't.  That means keyboard
responsiveness is percieved to be much better with
multi-processor systems.  So is X, because at any given time X
will be on one cpu and the cpu intensive program you run will be
on the other cpu.

My firewall and my laptop aren't SMP boxes, put it that way.

-- 
Floyd L. Davidson         <http://www.ptialaska.net/~floyd>
Ukpeagvik (Barrow, Alaska)                 floyd@barrow.com
 

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