Re: computing load averages

[Ben Russo <ben muppethouse com>]

Shragai, Yaron wrote:
> Hello,
> How are load averages computed for the top command and the /proc/loadavg
> file?  Where do the numbers come from?
>
> Thanks,
> Yaron


cat /proc/loadavg

These are numbers internal to the kernel.

They are 5, 10 and 15 minute average values
of the number of processes that are in a "run" state at each sample.

You should consider your load in reference to the number of CPU's you 
have in a system.  If you have 8 CPU's, then having a load of 7 isn't a 
problem.  If the load is higher than the number of CPU's then you should 
look at your top's CPU stats, and look at iostat and vmstat and sar.

A box can have a high load for several different reasons (or 
combinations of those reasons).  You may have a number of processes all 
running simultaneously and the CPU is just running as fast as possible 
(evidenced by less than 2% idle time shown in top for CPU usage).

You may have a number of processes that are in run states, but are 
waiting for data i/o  (evidenced by having abundant CPU idle time, but 
still having a load higher than the number of CPU's).

Check vmstat for memory swap activity, i/o activity

-Ben.