Kernel panic when unpluggin AC adaptor

[Kevin Oberman]

> Date: Wed, 12 May 2010 15:35:51 +0200
> From: David DEMELIER <demelier.david at gmail.com>
> Sender: owner-freebsd-stable at freebsd.org
> 
> Hi, I tested your patch and it didn't panic. I checked the dev.cpu
> sysctl nodes to see if the CPU freq is changing or not.
> 
> I unplugged the cable :
> markand at Melon ~ $ sysctl dev.cpu
> dev.cpu.0.%desc: ACPI CPU
> dev.cpu.0.%driver: cpu
> dev.cpu.0.%location: handle=\_PR_.CPU0
> dev.cpu.0.%pnpinfo: _HID=none _UID=0
> dev.cpu.0.%parent: acpi0
> dev.cpu.0.freq: 450
> dev.cpu.0.freq_levels: 2101/35000 1837/30625 1600/23888 1400/20902
> 1200/15000 1050/13125 900/11250 750/9375 600/7500 450/5625 300/3750
> 150/1875
> dev.cpu.0.cx_supported: C1/1 C2/1 C3/162
> dev.cpu.0.cx_lowest: C3
> dev.cpu.0.cx_usage: 0.00% 99.99% 0.00% last 131us
> dev.cpu.1.%desc: ACPI CPU
> dev.cpu.1.%driver: cpu
> dev.cpu.1.%location: handle=\_PR_.CPU1
> dev.cpu.1.%pnpinfo: _HID=none _UID=0
> dev.cpu.1.%parent: acpi0
> dev.cpu.1.cx_supported: C1/1 C2/1 C3/162
> dev.cpu.1.cx_lowest: C3
> dev.cpu.1.cx_usage: 0.00% 99.99% 0.00% last 260us
> 
> I plugged the cable :
> 
> markand at Melon ~ $ sysctl dev.cpu
> dev.cpu.0.%desc: ACPI CPU
> dev.cpu.0.%driver: cpu
> dev.cpu.0.%location: handle=\_PR_.CPU0
> dev.cpu.0.%pnpinfo: _HID=none _UID=0
> dev.cpu.0.%parent: acpi0
> dev.cpu.0.freq: 2101
> dev.cpu.0.freq_levels: 2101/35000 1837/30625 1600/23888 1400/20902
> 1200/15000 1050/13125 900/11250 750/9375 600/7500 450/5625 300/3750
> 150/1875
> dev.cpu.0.cx_supported: C1/1 C2/57
> dev.cpu.0.cx_lowest: C1
> dev.cpu.0.cx_usage: 100.00% 0.00% last 497us
> dev.cpu.1.%desc: ACPI CPU
> dev.cpu.1.%driver: cpu
> dev.cpu.1.%location: handle=\_PR_.CPU1
> dev.cpu.1.%pnpinfo: _HID=none _UID=0
> dev.cpu.1.%parent: acpi0
> dev.cpu.1.cx_supported: C1/1 C2/57
> dev.cpu.1.cx_lowest: C1
> dev.cpu.1.cx_usage: 100.00% 0.00% last 497us
> 
> Of course I enabled
> 
> # Little power management.
> performance_cx_lowest="HIGH"
> performance_cpu_freq=${performance_cx_lowest}
> economy_cx_lowest="LOW"
> economy_cpu_freq=${economy_cx_lowest}
> 
> in my /etc/rc.conf, it the behavior expected ?

I won't say that it is expected, but it is not unusual. It looks like
more and more laptops don't offer higher 'C' states when on AC power. My
ThinkPad gives me C3 on AC power and adds C4 on battery.

You have an awful lot of available frequencies. I really recommend
turning off TCC/Throttling, if they are active. They don't really save
power and can cause problems at low values. They also impact powerd's
responsiveness to changes in CPU load. What you REALLY want are the true
power management clock/voltage step which are usually between 2 and
6. My old T30 only had two. My not quite as old T43 has 5 ranging from
2 GHz down to 800 MHz.

I really wish TCC and throttling would be disabled by default or totally
removed. they were intended for thermal management, not power management.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751