"Interesting" behavior of ACPI power management on T43 with CURRENT

Kevin Oberman oberman at es.net
Thu Jul 19 23:45:21 UTC 2007


My system seems to have grown added power management capabilities
without cpufreq and maybe powerd. The behavior of my laptop (Lenovo/IBM
T43) as regards power management with CURRENT is suddenly very
different. I am pretty sure that this behavior first appeared in the
past few months, so come change in FreeBSD (probably in ACPI code)
triggered the change.

Adding cpufreq to the system really breaks a lot of things since the
module mis-identifies my system and sets all of the values for freq
wrong. (It lies as I have confirmed that it is running at 2GHz when
FreeBSD claims it is running 1.5 GHz and loses all of the energy
values. They show up as -1.

My system has a 2GHz Pentium-M CPU. I am not loading cpufreq or
anything else specificly targeted at power management, but I do run the
Gnome Power Manager which may be involved.

I have no ACPI related items built into the kernel. Here is a list of
loaded modules:
kernel
vesa.ko
geom_eli.ko
crypto.ko
zlib.ko
linux.ko
snd_ich.ko
sound.ko
acpi_video.ko
acpi.ko
wlan_scan_sta.ko
acpi_ibm.ko
wlan_wep.ko
if_ath.ko
ath_rate.ko
ath_hal.ko
logo_saver.ko
radeon.ko
drm.ko
ntfs.ko

cpufreq.ko is not there.

On AC power I see:
dev.cpu.0.freq: 2000
dev.cpu.0.freq_levels: 2000/27000 1750/23625 1600/22600 1400/19775 1333/19666 1166/17207 1066/16733 932/14641 800/13800 700/12075 600/10350 500/8625 400/6900 300/5175 200/3450 100/1725
dev.cpu.0.cx_supported: C1/1 C2/1 C3/85 C4/185
dev.cpu.0.cx_lowest: C1
dev.cpu.0.cx_usage: 100.00% 0.00% 0.00% 0.00%

On battery:
dev.cpu.0.freq: 2000
dev.cpu.0.freq_levels: 800/13800 700/12075 600/10350 500/8625 400/6900 300/5175 200/3450 100/1725
dev.cpu.0.cx_supported: C1/1 C2/1 C3/85 C4/185
dev.cpu.0.cx_lowest: C4
dev.cpu.0.cx_usage: 0.00% 46.33% 0.94% 52.71%

After a while, the value of dev.cpu.0.freq will drop to 800, but it can
take a while. I suspect that this is simply the sysctl not getting
updated when the maximum clock speed is dropped top 800 MHz. (this kind
of implies powerd is NOT involved in all of this.)

My CPU acts like it is under control of powerd, but:
  762  ??  Ss     0:01.06 /usr/sbin/powerd -a maximum

In the past, I saw a maximum speed of 2GHz on either AC or battery and
my system never dropped the CPU speed while on AC.

This changes has really improved the battery life of my system and I
like it, I am simply baffled as to why it is doing it and if it is
ThinkPad specific or if others are seeing this.
-- 
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
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