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

[Russell King <rmk+lkml@arm.linux.org.uk>]

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