[wplug] cpu load?

[Jonathan S. Billings]

On Thu, Aug 16, 2007 at 12:34:13AM -0400, Zach wrote:
> xload is showing my CPU at 90-100% usage for the past 20 minutes and
> my system is very slow and I see my green disk activity light blinking
> furiously yet when I look in top or ps I see no process with more than
> 3% CPU and all of the processes combined are using less than 10% of
> the CPU. Is there a more accurate and up to date way to see precisely
> the real CPU load and which process is using the most. Something like
> the Sysinternals Process Explorer (I think Microsoft bought them out).

Keep in mind -- xload does *NOT* show your CPU usage.  It shows a
histogram of the *system load average*.  The system load average
is the same value provided by 'uptime' (displayed in 1 minute, 5
minute and 15 minute intervals).  

Load average is a fairly poorly understood (and poorly documented)
attribute in linux.  As other posters have mentioned, it is the
average length of the CPU run queue.  There are a variety of things
that can increase the load average, and the most obvious is what I see
here:

> root     19180  0.7  0.3   1980   824 pts/0    D+   00:17   0:07 updatedb

See the D+ there?  That means that when you ran 'ps', it was in
"Uninterruptible sleep (usually IO)" (according to ps's man page).
Every process that is waiting on I/O can easily increase your load
average.  If I recall correctly, every process that's in
uninterruptible sleep increases the load average by one, so if you
have 32 processes in that state, your load average is increased by
32. 

-- 
Jonathan Billings
billings at negate.org