High interrupt load on VIA C3 machine

[Bruce Cran]

Peter Jeremy wrote:
> On 2007-Sep-01 23:56:30 +0100, Bruce Cran <bruce at cran.org.uk> wrote:
>   
>> The VIA C3 supports 2 frequencies - 531 and 265 MHz.  The high interrupt 
>> load only occurs when I set dev.cpu.0.freq to 265, which makes sense.
>>     
>
> Half the clock rate implies twice the interrupt load - it it should be
> about 3.5% at 531MHz if its 7% at 265MHz.  If you're seeing something
> significantly different then there is some other factor at work.
>
>   

It seems there is something different happening, but I don't know if 
it's to do with FreeBSD or just the way the CPU works. 
At 531MHz the "swi4: clock sio" task uses 0.2% CPU and the "interrupt" 
line in top goes up to about 1.6%.  
At 265MHz the "swi4: clock sio" task uses about 10% CPU and the 
"interrupt" line varies between 14 and 20%.

--
Bruce Cran