Defining Unix Load Average
November 7, 2005 | 5 Comments
Went looking for a simple definition of load average in Unix, but alas, simplicity is not in the nature of load. I read UNIX® Load Average Part 1: How It Works by Dr. Neil Gunther who breaks load down into much appreciated, yet excruciating detail.
In short it is the average sum of the number of processes waiting in the run-queue plus the number currently executing over 1, 5, and 15 minute time periods.
It’s calculated like this: load(t) = load(t - 1) e^(-5/60m) + n (1 - e^(-5/60m))
(at least in Linux)
From Gunther’s PDF Guide:
Most sys admins tend to refer to and use the m = 1 minute load average For queueing models we want the steady-state average [...] that suggests the m = 15 minute load average is more useful for capacity planning
So load is useful but complex.
Casey experienced some pretty sever load numbers recently…
Tags: definition, dr. neil gunther, gunther, LA triplets, linux top, load, load average, monitoring, performance, performance monitoring, solaris, unix