VIA EPIA 5000 and ACPI Cx levels

[Bruce Cran]

On Sunday 10 October 2010 21:49:30 b. f. wrote:

> If it has an i8254, that can also be used in one-shot mode if
> hint.attimer.0.timecounter=0 is used, since r212778.  

Thanks, I didn't know about that. After enabling it things are quite 
different: kern.eventtimer.periodic is now 1, and setting 
hw.acpi.cpu.cx_lowest=C2 results in 100% time being reported as being spent in 
C2 mode according to dev.cpu.0.cx_usage - using C3 causes the system to hang.  
Shouldn't a fully loaded CPU spent more time in C1 state though? When I run a 
program that results in 0% idle time cx_usage still reports that no time was 
spent in C1 state.

> But for low
> values of kern.hz, I've found that periodic mode can result in fewer
> interrupts (albeit increased latencies and lower accuracy in
> accounting) than one-shot mode, if kern.eventtimer.singlemul=1.  As
> for the power-saving states, are you using a simple 'sysctl
> dev.cpu.0.cx_usage' to find the percentages? If you're doing
> something more involved, you may be affecting the measurements.  Also,
> does the system think that the deeper sleep states are available on
> your machine?  If so, what are their latencies?  If they are high,
> they may be used less often, or not at all.  

I'm just using dev.cpu.0.cx_usage to check the Cx level usage. According to 
dev.cpu.0.cx_supported, I have:

C1/0, C2/90, C3/900


> Did you follow some of
> the other recommendations to allow more sleeping, like at:
> 
> http://wiki.freebsd.org/TuningPowerConsumption

I haven't done anything extra yet, since I was mainly interested in seeing if 
one-shot mode worked on this box.  I can't use powerd because running at 
266MHz (I only have 533 and 266 available) results in too much of a slowdown.

-- 
Bruce Cran