improve cx_lowest logic

[Ian Smith]

On Tue, 10 Jul 2012 09:31:26 -0700, Sean Bruno wrote:
 > On Tue, 2012-07-10 at 07:27 -0700, Ian Smith wrote:
 > > I wonder if that explains why setting C3 on aforesaid T23 has no
 > > effect 
 > > (in terms of dev.cpu.0.cx_usage indicating any time spent in C3)
 > > unless 
 > > the machine happened to be booted up on battery, in which case C3 is 
 > > shown as working whenever its enabled, by power_profile or manually?
 > > 
 > > 
 > 
 > silly question, did you set these in /etc/rc.conf ??
 > 
 > performance_cx_lowest="LOW"
 > economy_cx_lowest="LOW"

Fair enough question.  For years, since 7.0-R, I've been running
 performance_cx_lowest=C2
 economy_cx_lowest=C3
but as reported yesterday, either way it wasn't actually using C3, and 
I'd checked it several times over maybe 20 minutes.

However, after (inadvertantly) leaving hw.acpi.cpu.cx_lowest manually 
set to C3 while on AC power overnight, this morning I discover:

dev.cpu.0.freq: 733
dev.cpu.0.freq_levels: 1133/19100 733/12500
dev.cpu.0.cx_supported: C1/0 C2/84 C3/120
dev.cpu.0.cx_lowest: C3
dev.cpu.0.cx_usage: 0.09% 11.29% 88.61% last 635us

So, hmm, C3 must have kicked in sometime later?  Now I can merrily 
change cpu.cx_lowest between C1, C2 or C3 and have that reflected in 
usage; now C3 on AC: dev.cpu.0.cx_usage: 0.03% 0.75% 99.21% last 683us

confused :), Ian