I quite like my Lenovo X201i laptop, I’ve been using it for a couple years now and it’s turned out to be the ideal combination of size and usability – the 12″ form factor means I can carry it around easily enough, it has plenty of performance (particularly since I upgraded it to an SSD and 8GB of RAM) and I can see myself using it for the foreseeable future.

Unfortunately it does have a few issues… the crappy “Thinkpad Wireless” default card that comes in it caused me no end of headaches and the BIOS has always been a

Thankfully most of the major BIOS flaws have been resolved in part due to subsequent updates, but also thanks to the efforts of the Linux kernel developers to work around weird bits of the BIOS’s behavior.

Sadly not all issues have been resolved, in particular, the thermal management is still flawed and fails to adequately handle the maximum heat output of the laptop. I recently discovered that when you’re unfortunate enough to run some very CPU intensive single-threaded processes, by keeping 1/4 cores at 100% for an extended period of time the Lenovo laptop will overheat and issue an emergency thermal shutdown to the OS.

During this time the fan increases in speed, but still has quite a low noise level and airflow volume, which is very hot to the touch, it appears the issue is due to the Lenovo BIOS not ramping the fan speed up high enough to meet the heat being produced.

Thanks to the excellent Thinkwiki site, there’s detailed information on how you can force specific fan speeds using the thinkpad_acpi kernel module, as well as details on various scripts and fan control solutions people have written.

What’s interesting is that when running the fan on level 7 (the maximum speed), the fan still doesn’t spin particularly fast or loudly, no more than when the overheating occurs. But reading the wiki shows that there is a “disengaged” mode, where the fan will run at the true maximum system speed.

It appears to me that the BIOS has the 100% speed setting for the fan set at too low a threshold, the smart fix would be to correct the BIOS so that 100% is actually the true maximum speed of the fan and to scale up slowly to keep the CPU at a reasonable temperature.

In order to fix it for myself, I obtained the tp-fan program, which runs a python daemon to monitor and adjust the fan speeds in the system based on the configured options. Sadly it’s not able to scale between “100%” and “disengaged” speeds, meaning I have the choice of quiet running or loud running but no middle ground.

Thanks to tpfan’s UI, I was able to tweak the speed positions until I obtained the right balance, the fans will now run at up to 100% for all normal tasks, often sitting just under 50 degrees at 60% fan speed.

When running a highly CPU intensive task, the fan will jump up to the max speed and run at that until the temperature drops sufficiently.  In practice it’s worked pretty well, I don’t get too much jumping up and down of the fan speed and my system hasn’t had any thermal shutdowns since I started using it.

Whilst it’s clearly a fault with the Lenovo BIOS not handling the fans properly, it raised a few other questions for me:

• Why does the OS lack logic to move CPU intensive tasks between cores? Shuffling high intensive loads between idle cores would reduce the heat and require less active cooling by the system fans – even on a working system that won’t overheat, this would be a good way to reduce power consumption.
• Why doesn’t the OS have a feature to throttle the CPU clock speed down as the CPU temperature rises? It would be better than having the all or nothing approach that it currently enforces, better to have a slower computer than a fried computer.

Clearly I need some more free time to start writing kernel patches for my laptop, although I fear what new dangerous geeky paths this might lead me into. :-/