High interrupt load on VIA C3 machine

[Bruce Cran]

Peter Jeremy wrote:
> On 2007-Aug-31 20:52:58 +0100, Bruce Cran <bruce at cran.org.uk> wrote:
>   
>> This appears to be an issue with powerd/cpufreq - disabling powerd reduces 
>> the interrupt load to a couple of percent at most, and the clock interrupt 
>> task now only accumulates CPU time very slowly (previously it was using 7% 
>> CPU all the time).
>>     
>
> I'm not familiar with the VIA CPUs but how slowly can powerd make the
> CPU run?  The top extract you posted show the system was idle so its
> likely that powerd had wound the clock to a minimum.  The amount of
> code executed by the interrupt handlers remains the same but will take
> longer at slower clock speeds so the percenatage is higher.
>
> You can experiment for yourself by enabling only cpufreq and using
> sysctl.  dev.cpu.0.freq_levels lists all supported possible CPU rates
> and you can change the clock frequency by assigning dev.cpu.0.freq.
>   

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.

--
Bruce Cran