Squeezing the watts

Saturday, August 4th, 2007 at 3:05 pm | 681 views | trackback url

I’ve written a couple of previous posts about saving power around the office and home, and have been using my Watts-Up Pro power analyzer/data logger to measure every power-enabled device that I use.

In that range, I’ve been tweaking the kernel on my Thinkpad T42p to minimize the power consumption of it during running hours. Here’s some things I’ve found:

Enable these kernel options:

# Set the kernel to only use the CPU speed that is appropriate to the load. 
# If you're reading email, there's no reason for your 2.4Ghz processor to 
# be running at that speed, so train it down to 600Mhz instead, etc.
CONFIG_CPU_FREQ_GOV_ONDEMAND

# Use the new, "next generation" high-performance timer instead of the
# legacy 8254s. 
CONFIG_HPET_TIMER

# The in-kernel irq balancer is obsolete and wakes the CPU up far more 
# than needed.
CONFIG_IRQBALANCE

# This is required to set longer CPU sleep times in the kernel
CONFIG_NO_HZ

# This enables the aggressive power-saving support of  the AC97 sound 
# codecs.  In this mode, the power-mode is dynamically controlled at each
# open/close. This will save roughly ½ watt of power.
CONFIG_SND_AC97_POWER_SAVE

# This automatically disables UHCI USB when not in use. This saves 
# roughly 1 Watt of power.
CONFIG_USB_SUSPEND

And add these tweaks to your startup scripts:

# Wake up the disk less often
echo 1500 > /proc/sys/vm/dirty_writeback_centisecs

# Enable laptop mode
echo 5 > /proc/sys/vm/laptop_mode

# Enable powersave mode for AC97
echo 1 > /sys/module/snd_ac97_codec/parameters/power_save

After you set these and rebuild your kernel with those options, you should now be consuming a lot less power than the “stock kernel”. Good luck!

Last Modified: Saturday, August 4th, 2007 @ 15:05

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