vfand: A daemon to control fan speed in Vaio laptops
27 July 2010
Today I got tired of getting frequent lock-ups in my laptop, a Vaio
TZ11MN/N which has been serving me just fine the during the past
three years. I decided to investigate a bit because the machine was
quite hot, and after some digging I found that the fan speed was being
kept below 45, by reading from
/sys. For example:
cat /sys/devices/platform/sony-laptop/fanspeed 44
Then I noticed that writing to the file would also work, but the embedded controller would insist in lowering the speed, so I ran the following loop from the shell:
while sleep 5 ; do echo 200 > /sys/devices/platform/sony-laptop/fanspeed done
That snip caused the fan to stay running at a higher speed, and the laptop temperature started to fall slowly. Then I tried fancontrol, without luck: the fans in my TZ11 cannot be controlled with it. Then I decided to write my own, and vfand was born.
Even when some temperature sensors are there (e.g. the one in the CPU
die), I found no easy way of determining the overall temperature of
the machine using entries from
/sys. Next was to determine which
driver is in charge of the fan entry under
/sys, to check whether it
can do something else. The fan entry is managed by the sonypi
driver, which actually does support opening
/dev/sonypi and getting
the temperature using an
SONYPI_IOCGTEMP. It looked
fine, so I implemented my little daemon in terms of
ioctl on that
device, so it should would with all Vaio laptops supported by the
The speed control algorithm is quite simple at the moment, but it works fine for me:
- When the temperature is less than a user-configurable value (35º C by default), the fan speed is set to the minimum possible value.
- When the temperature is above a user-configurable value (55 ºC by default), the fan speed is set to the maximum possible value.
- If the temperature is in between the configurable values, then a linear formula is used to calculate the speed. As the temperature raises, the fan speed will be raised, too (and vice versa).
The daemon is naïve, so it will log errors to the standard error stream,
and it will not detach itself from the controlling terminal. An option
is running it from
/etc/rc.local until I add an init script which uses
start-stop-daemon (or something else) to launch it.
Another option, which is a bit bizarre but will ensure that it is always running even if it does, is doing:
echo 'vf:2345:respawn:/usr/bin/vfand' >> /etc/inittab telinit q
Last, but not least, I have already uploaded a simple, working package to our APT repository.
I hope this is useful for some other Vaio users out there.