load averages

[Ryan Thompson]

Paulo Roberto wrote to freebsd-questions at freebsd.org:

> Hello,

Hi Paulo,

> Is the "load averages" field in uptime/top in percentage??

No. The load averages represent the number of processes in the run
queue (i.e., the number of processes that are ready to run, but must
wait for CPU time). Load averages > 1.00 are normal.

I haven't seen this discussion on here for awhile, so I'll explain
further.

Load averages are only loosely correlated with system performance. It
is possible to have relatively high load averages, and still have a
very responsive system. It is also possible to have load averages
below 0.50 on a disk-bound machine, and have an unusable machine.
(I've seen both). It is also possible to inadvertently write a fork
bomb (in Perl) and watch them peak at about 600, and still manage to
obtain a sort-of-responsive root login to kill all of the processes.
(Uh.. I've *never* seen that happen).

Again, load average is a function of the number of processes waiting
for CPU time. *Not* of actual CPU utilization (which will often be
quite a bit lower than 100%), or of overall resource utilization
(disk, net, etc.) Use load averages for only a very rough sanity
check.

- Ryan

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  Ryan Thompson <ryan at sasknow.com>

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