# Reconciling Load Average and Percentage Idle

• 10-04-2007, 12:35 AM
unix
Reconciling Load Average and Percentage Idle
I have a 16-core p570 running an IBM Informix database, and very little
else. I sense it's currently substantially over-specd, even at the buiest
times.

During these busy times the Load Average (as measured by uptime say) rises
to as high as 3.50. yet the "Percentage Idle" as monitored via topas never
dips below 85%. How can this be? If the processors are that idle how can I
be building up a queue on them?

thx
Neil

• 10-04-2007, 12:35 AM
unix
Re: Reconciling Load Average and Percentage Idle
On Mon, 25 Dec 2006, Neil Truby wrote:
[color=blue]
> I have a 16-core p570 running an IBM Informix database, and very little
> else. I sense it's currently substantially over-specd, even at the buiest
> times.
>
> During these busy times the Load Average (as measured by uptime say) rises
> to as high as 3.50. yet the "Percentage Idle" as monitored via topas never
> dips below 85%. How can this be? If the processors are that idle how can I
> be building up a queue on them?[/color]

3.5/16 = 0.21

-s
• 10-04-2007, 12:35 AM
unix
Re: Reconciling Load Average and Percentage Idle
>[color=blue]
> 3.5/16 = 0.21
>[/color]

Exactly.
A more verbose comment would have been more helpful for Neil though.

"The load average is the number of runnable processes over the
preceding 1-, 5-, 15-minute intervals."
What this means loosely is that the system would be 100% busy when load
average equals the number of runqueues (i.e., #cpus, which is 16 in

A load avg of 3.5 means only 21% busy system...so topas correctly
reported system idle-ness.

• 10-04-2007, 12:35 AM
unix
Re: Reconciling Load Average and Percentage Idle
<kcnainwal@gmail.com> wrote in message
> >
>> 3.5/16 = 0.21
>>[/color]
>
> Exactly.
> A more verbose comment would have been more helpful for Neil though.
>
> "The load average is the number of runnable processes over the
> preceding 1-, 5-, 15-minute intervals."
> What this means loosely is that the system would be 100% busy when load
> average equals the number of runqueues (i.e., #cpus, which is 16 in