Re: [Condor-users] What is "the CPU hour"?

[Ian Chesal <ICHESAL@xxxxxxxxxx>]

> When browsing through Condor articles, often the term "CPU hour"
appears.
> Am I right that this is a somewhat sloppy computational unit?

Sloppy -- that's not a bad word. It's the work done by a CPU in one hour
of wall clock time. So yea, it doesn't tell you much because of
variances in the processing capabilities of chips.

> Are the following two statements then correct?
>
> 1) The CPU hour does not tell you how much work can be done, as this
also
>    depends (among many other things) on the speed of the CPU; one CPU
>    hour on a 1 GHz CPU does much less work, than one CPU hour on a
>    3 GHz CPU.

Correct. Sometimes you'll see CPU hour times normalized when you're
doing cross-machine comparisons so you *can* tell how much work can be
done.

For example: we rate our machines based on a normalized CPU hour metric.
The slowest machine in our pool has a speed rating of 1. The faster
machines are all rated based on their ability to do more work in a CPU
hour than the slowest machines. A machine with a rating of 2 can do
twice as much work in a CPU hour (more or less, assumes CPU-constrained
job) as a machine with a 1 rating.

> 2) How many CPU hours are created by Condor, is a measure of how
effective
>    Condor is converting otherwise wasted computational resources.
>
> In other words: the amount of CPU hours says more about Condors
abilities,
> than about the potential amount of work that can be done.

I don't agree with this statement. Condor is very good at making CPU
available according to the policy you've set up. As long as there's jobs
in the queue and machines available Condor can turn that into useful
work time with very, very little overhead. CPU hours say more about your
policies and the use patterns of the users on your machines than
Condor's ability to harvest unused cycles.

- Ian

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