Machine slow

[Billy A. Pumphrey]

I have the MailScanner book :)

Billy Pumphrey
IT Manager
Wooden & McLaughlin
> -----Original Message-----
> From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK] On
> Behalf Of Steen, Glenn
> Sent: Thursday, May 19, 2005 3:10 AM
> To: MAILSCANNER at JISCMAIL.AC.UK
> Subject: Re: Machine slow
> 
> Julian Field wrote:
> > 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.
> 
> It was just an example Julian. To be more precise the "unconditional
1"
> is added per process in state D (non-interruptible wait state) which
> _usually_ means some form of IO wait, but can be other things... As
> you already know, of course:-).
> 
> Sole purpose of the example was to make Billy go buy not only your
> MS book, but also the (in my view) excellent swordfish book too.
> It's a friend to bring to the WC, trainride and nightstand....:-):-)
> Your (as usual) excellent explanation should bring the point over.
> 
> Cheers
> -- Glenn
> 
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