System monitor: what does "Load average" exactly cover ???

[David Fox]

On Sat, Jun 7, 2008 at 10:14 AM, Vincent Trouilliez
<vincent.trouilliez at modulonet.fr> wrote:
> Hi,
>
> In the system monitor, at the top of the "Processes" tab, it says:
>
> " Load averages for the last 1, 5, 15 minutes: 0.09, 0.16, 0.18 "

It's the average of processes that are runnable, i.e., not sleeping,
in the last 1, 5, and 15 minutes.

In other words, this is the number of processes actually running on
your system at those times. But if you look at top, or ps, you'll see
a lot of processes in S state (sleeping) or in D state (waiting on
disk input). Processes that are in those states are not doing
anything, but waiting for something else to happen. When it does, then
they'll wake up (if only for less than a second sometimes) and that
will contribute to a larger load average, at least momentarily.

> That's the problem: after nearly 4 years of using Ubuntu/Gnome, I still
> haven't found an easy/logical explanation to these ridiculously low
> numbers, that never seem to get past 0.50 nevermind 1.00.

That seems about right, but it is only dependent on your usage. If
you're not running a whole lot of processes (I mean actively running)
then the load average should not go up that much, and if you're
running something constantly in the background like seti at home then
the load average will constantly be above 1, because that process is
always running (or almost always, since when the system becomes idle
it takes over).


> Usually by "system load" one refers to CPU load, but that can't be
> that, as the figures should rather be two orders of magnitude higher
> than that.

If that were true, your system would suddenly keel over and die. :)

The highest I've ever been able to load the system up that high -
i.e., over 100 - is when doing a huge make -j 256 or something on the
linux kernel. That is fun, it generates a lot of processes running -
like 256 copies of the C compiler all trying to run at once.

It makes for a reasonably good system stability test, but I wouldn't
try it too much, as your other sessions would respond so slowly (like
wait 10 minutes for an 'ls' output to come back - it would remind me
of my days in cobol class when I had to wait for hours for a compile
to come back.) Ouch....


> Maybe a mix of CPU + RAM + swap space + network B/W ?

Load average has nothing to do with RAM/swapspace/network. There are
other methods to gauge such usage, and gnome system monitor is a good
start. For instance, if you see the CPU line gauges, that is a pretty
good indicator of how busy your CPU is. FWIW my cpu percentage (on a
dual core amd64) is pegging close to 100%, and my load average is
closer to 8-10 right now. But then I'm torrenting and doing a video
conversion at the same time.

top is good too as an indicator of what processes are hogging the cpu(s).