Machine slow

[Julian Field]

On 18 May 2005, at 15:48, Steen, Glenn wrote:

> Billy A. Pumphrey wrote:
>
>> Quick verification on load average if I may.
>>
>> I do not understand how those numbers work.  They appear not to be
>> percent usage.
>>
>> How do the load average numbers work?
>> On my mailwatch, my usually is around .60-1.4
>>
>> Billy Pumphrey
>> IT Manager
>> Wooden & McLaughlin
>>
>>
> (snip)
>
> The "load factors" are perhaps the most abused "performance
> statistics"
> around... They're just the CPU run queue size (+ running jobs)
> averages
> calculated for 1, 5 and 15 minutes. Nice to know and a quick
> indicator,
> but nothing else.
>
> For example: on a one CPU system a load of 2 might be less than
> desirable,
> while on a system with 4 CPUs it shows two CPUs idling away... So one
> needs weigh the system as a whole when determining if a certain
> load is
> fine or not.

It's not as simple as that. Jobs can be in the run queue if they are
waiting for disk or network response. So if you have 10 processes all
waiting to do DNS lookup, for example, then you will have a load
greater than 10, but totally idle CPU(s).

This is why a busy MailScanner having a load of up to about 15 is
nothing to worry about. It merely means there are 15 processes
waiting for any of
     (a) CPU time
     (b) network response
     (c) disk i/o.
And that is a very simple view of it.

When the figure is over 1, it really doesn't tell you very much of
any use at all. And all it tells you when it is less than 1 is that
there is some time when your system is not doing anything.

--
Julian Field
www.MailScanner.info
Buy the MailScanner book at www.MailScanner.info/store
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