Re: High load average on disk I/O on 2.6.17-rc3

From: Russell King
Date: Mon May 08 2006 - 07:28:16 EST


On Mon, May 08, 2006 at 01:22:36PM +0200, Arjan van de Ven wrote:
> On Mon, 2006-05-08 at 13:13 +0200, Erik Mouw wrote:
> > On Sun, May 07, 2006 at 09:50:39AM -0700, Andrew Morton wrote:
> > > This is probably because the number of pdflush threads slowly grows to its
> > > maximum. This is bogus, and we seem to have broken it sometime in the past
> > > few releases. I need to find a few quality hours to get in there and fix
> > > it, but they're rare :(
> > >
> > > It's pretty harmless though. The "load average" thing just means that the
> > > extra pdflush threads are twiddling thumbs waiting on some disk I/O -
> > > they'll later exit and clean themselves up. They won't be consuming
> > > significant resources.
> >
> > Not completely harmless. Some daemons (sendmail, exim) use the load
> > average to decide if they will allow more work.
>
> and those need to be fixed most likely ;)

Why do you think that? exim uses the load average to work out whether
it's a good idea to spawn more copies of itself, and increase the load
on the machine.

Unfortunately though, under 2.6 kernels, the load average seems to be
a meaningless indication of how busy the system is from that point of
view.

Having a single CPU machine with a load average of 150 and still feel
very interactive at the shell is extremely counter-intuitive.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
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