On Mon, Aug 13, 2007 at 03:54:15PM +0930, Edwards, David (JTS) wrote:
> Hi,
>
> On a multiprocessor box, I'm seeing the following loads.
>
> top:
> load averages: 1.18, 1.17, 1.16
> 15:48:11
> 49 processes: 48 idle, 1 on processor
> CPU0 states: 2.8% user, 0.0% nice, 0.6% system, 0.0% interrupt,
> 96.6% idle
> CPU1 states: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt,
> 100% idle
> CPU2 states: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt,
> 100% idle
> CPU3 states: 0.2% user, 0.0% nice, 0.0% system, 0.0% interrupt,
> 99.8% idle
>
> uptime:
> 3:48PM up 15 days, 19:59, 2 users, load averages: 1.15, 1.17, 1.16
>
> These seem like high average loads to me but the server is idling (as
> shown by CPU usage in top).
Well, aside from the 'the load average is useless anyway' comments, a
load average of 1 is not necessarily unacceptable on a multi-processor
machine. (It means one CPU is constantly working.)
> I understood that load averages were related to the number of processes
> in the run-queue (i.e. waiting to get some processor time) so average
> loads above 1 would show a processing bottleneck.
>
> Did I get this wrong? If so, what do the load averages show and what
> would be a high load for a dual CPU (4 core) system?
That depends on a lot of things - most of which can not be read from the
load average - but as a data point, the system I'm typing this on is a
uniprocessor box. The CPU is 96% idle. The load average is 3 (backups
and checking out the OpenBSD tree from a local repository - i.e. the
bottleneck is the disk and the network, not the CPU). The system is
pretty responsive.
However, if we are talking CPU-bound processes, anything less than 4 at
a time means that there is no (significant) contention for the bounding
resource, which roughly means they all run at full speed. This is not to
say that having some reserve capacity is not useful, or that you should
strive for 100% resource utilization, but running one CPU-bound process
is not a high load for this machine. (One disk-bound process, on the
other hand, may be.)
Joachim
--
TFMotD: netstat (1) - show network status
