[2426] in Consulting_FYI
Meaning of "Load Average"
jfc@ATHENA.MIT.EDU (jfc@ATHENA.MIT.EDU)
Tue Oct 17 02:11:16 1989
[mail to cfyi got "Can't enter transaction into /usr/spool/discuss/cfyi: Unknown code dsc 7"]
The online manual for "stty" on the vax includes the following:
BUGS
Nobody understands what the "load" means.
This statement is true in the sense that most users don't know what
the load average is, but it is possible to discover its meaning in
only a few thousand pages of documentation.
The "load average" is defined as the average number of processes in the
runnable queue or short term wait. Translated into english, this means
the number of jobs which are running or waiting on disk I/O. So, if you
have a program crunching numbers in the background, your load is unlikely
to drop below 1. If you are compiling something, your load may reach 5 (1
for the compiler, and 4 more for the background processes that handle file
access over the network). On the other hand, if you are doing nothing but
typing into emacs, your load is unlikely to rise above .1 (since emacs
waiting for you to press another key does not count in the load average).
Load average for the same set of processes will vary among machines
depending on the speed of the machine, the amount of memory, the state of
the network, etc.
The number in [] after the load average on the emacs status line is a
measure of local disk I/O. I am not sure what the exact units are (I
think it is number of disk reads or writes per second). This is unlikely
to be useful information to most users (on an RT in a public cluster, you
can get a better estimate by listening to the drive).
--John Carr
