A niggle about linearity

Posted May 13, 2011 20:05 UTC (Fri) by dlang (guest, #313)
In reply to: A niggle about linearity by jberkus
Parent article: Scale Fail (part 1)

that only works if you know what those thresholds are.

in many cases they are not where you expect them to be (the hyperthreaded cpu utilisation is one example, locking overhead with multiple processors is another)

frequently there are factors in play that you don't know about, and the result is that until you test it to a particular load, you have no way of knowing if the system will reach that load.

interpolation (guessing how things work between measured points) is fairly reliable

extrapolation (guessing how things will work beyond measured points) is only reliable until some new factor shows up.