

UNIX Load Average Part 1: How It Works - nickb
http://www.teamquest.com/resources/gunther/display/5/

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jrockway
Good article, but one nit. This graph is weird:

<http://www.teamquest.com/images/gunther/ldavg1/LAFull.gif>

It's hard to understand because the lines represent minutes (1 minute, 5
minute, 15 minute load averages) but the x-axis is in seconds. That means I
have to divide by 60 in my head, which is a lot of unnecessary work.

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patrickg-zill
Just a note: you cannot usefully compare load averages between different Unix
OSes. For instance, running the same workload on a Solaris system and a Linux
system, then using load average as a measure of performance between the two,
is not going to give you any useful information.

~~~
SwellJoe
To expand upon this, you also cannot usefully compare load between two
applications of the same type. e.g. comparing the load averages of Apache vs.
LigHTTPD vs. nginx, is not useful. Depending on the architecture of the
application, such as threaded, forked, select/poll-based, or event-based, and
configuration, you may find significantly different load numbers, even if all
are performing identical tasks and with identical "performance".

For example Squid, in its aufs configuration (which uses threads for disk IO),
can exhibit extremely high load averages (>5) on even a moderately loaded
system. It'll still be performing fine, and you may still have significant
headroom for handling requests. But it looks really high, on Linux systems.
Even the filesystem on which a service is running can make a difference. Load
looks higher on a ReiserFS-based system running Squid than an Ext3
filesystem...and yet the Reiser system would handle more load (I guess it just
doesn't hide the evidence of its work very well).

