[wplug] Understanding Load

[Nicholas A. Schembri]

In the wikipedia  artical they site the paper on "Unix load Average".  That
paper talks about, " when two hot processes are running, the maximum load
is two (not one) on a single CPU."

They also quote, "
 ... High load averages usually mean that the system is being used heavily
and the response
time is correspondingly slow."

The goal is to gage system load.  A system is fully loaded when the system
scheduler always has something to run, ie a load of 2 x cores.  I've seen a
system with a load of 800 on a single core that was responsive. It's just a
gage you can watch.  Match how the system feels with the task at hand.  I
now think about power usage more then the cost of another box. I'm now over
the tipping point. VM are now good enough for my workloads.

http://en.wikipedia.org/wiki/Load_%28computing%29
Neil J. Gunther <http://en.wikipedia.org/wiki/Neil_J._Gunther>. "UNIX Load
Average – Part 1: How It
Works"<http://www.teamquest.com/pdfs/whitepaper/ldavg1.pdf>(pdf).
TeamQuest.
Retrieved 2009-08-12.[note
1]<http://en.wikipedia.org/wiki/Load_%28computing%29#cite_note-1>
http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages


Today's systems the disks are the slowest part.  I've noted poor
performance under low system load and High i0.  The following might help.
http://www.sysxperts.com/home/announce/vmdirtyratioandvmdirtybackgroundratio
http://rackerhacker.com/2008/08/07/reduce-disk-io-for-small-reads-using-memory/


Nicholas.A.Schembri