f9: question on load average

[Patrick O'Callaghan]

On Mon, 2008-09-15 at 17:09 +0200, Dario Lesca wrote:
> Il giorno lun, 15/09/2008 alle 10.04 -0430, Patrick O'Callaghan ha
> scritto:
> 
> > "Load average" is a running average of the number of ready processes,
> > i.e. those that could do something if they had the cpu. Processes that
> > are waiting for something to happen, e.g. I/O to complete, can't use the
> > cpu even if it's idle. Thus it's perfectly possible to have the cpu
> > doing nothing while the load average is high. It often means you have
> > some long I/O operation on a slow disk system e.g. copying a DVD to an
> > external USB device, or multiple downloads waiting for data to arrive
> > from the net.
> 
> Thanks Patrick!
> 
> There is a command for see, in this case, what's the process that is
> causing the hight Load Average?

It's not one process, it's caused by the set of processes on your system
in relation to the system's capabilities. The fact that there's a high
LA simply means that a lot of processes spend a lot of time waiting for
slow events. You can get an idea of which ones they are by looking at
the output of "ps axl". The STAT column shows process state; if it's 'D'
then the process is blocked on some event that might take a long time,
such as disk or network I/O. The WCHAN column shows the specific reason
for the wait (it's generally the address of a kernel data structure),
but you need to be familiar with kernel sources to really understand it.

Here's a pretty good explanation with some extra detail:
http://www.andymillar.co.uk/blog/index.php/2006/12/24/geekery/linux-load-average-explained/

Here's a more technical explanation of how the LA is calculated:
http://www.linuxjournal.com/article/9001

> In my case I discovered that the problem was caused by a remote NFS
> mounted with the remote NFS server out of office (my notebook).

That would probably do it :-)

poc