[mythtv-users] how to interpret loadaverage on mythtv backendstatus page

[chris at cpr.homelinux.net]

On Tue, Oct 04, 2005 at 09:35:20AM +0200, anders smith wrote:
> how do I interpret loadaverage on mythtv backendstatus page or when running
> top?

The numbers indicate the smoothed average number of processes running 
and waiting over a 1, 5, or 15 minute period.  If your machine has one 
single-core processor then a load average of 1.00 suggests that the CPU 
is running at or below 100% capacity over the specified time period.

Assume, for example, that you have two CPU-intensive processes that 
each take 30 seconds to complete.  If you start one and wait for it to 
finish before starting the other then there is always one process 
running and non waiting (from the system's POV) so the one-minute load 
average is 1.0.  If you start them at the same time then either of two 
things can happen: if one executes exclusively while the other waits, 
then your CPU queue is 2 for the first 30 seconds and 1 for the next 30 
seconds, and the one-minute load would be approximately 1.5 (because 
there was always one process running and for half the time there was a 
process waiting).  If the two processes share the CPU equally then each 
will take 60 seconds to complete, and the one-minute load average will 
be 2.0 (because there is always one running and one waiting).  The work 
processed in 60 seconds was identical in all three cases, however the 
sequential tasking provided data earlier for one process.

The first number (1-minute average) is a good indicator of real-time 
response.  If it gets high then you will "feel" bogged down.  The 3rd 
number (15-minute average) is a good indicator of long-term 
utilization.  The range of acceptable values will depend on the 
system's usage.  For example, running SETI in the background as a very 
low priority process will still drive up the load average without 
significantly affecting the system's response to foreground loading.

> I usually get numbers around 4, but is that good or bad (when grabbing and
> inserting it runs up to 6)?

It depends. :-P  Those numbers would be very high for a P-II or P-III 
but not so bad if you have a multi-CPU and/or multi-core system.

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