Before purchasing ThinkPad X280, I was concerned about the CPU throttling bug. It’s a bug which will throttle the CPU performance once it’s been triggered and will not restore the performance without a reboot.
I’ve developed a Ruby script for this test, and run it on X280 with i5-8250U processor. I did not reproduce the throttling issue that requires a reboot to restore the performance – whether the machine is powered by battery or connected to the power supply. However, I did discover a symptom which will under-clock the process to 123MHz under the certain load.
The Test
The test starts with a single instance of ‘benchmark‘ and starts another instance every 5 minutes. Leave the 4 instance running for 10 minutes, and start to kill each instance every 5 minutes.
The script will output detailed log to stdout and a summary to stderr. By consolidating the log and visualise it, we can see the correlation between the performance, CPU clock, fan speed and thermal readings.
Test Result
With power adaptor connected
Running on battery
The performance drops after the 3rd instance have been initiated. Let’s have a closer look at the performance.
With external power
On battery
It has the same behaviour, whether external power has been supplied or not. 42 seconds after starting the third instance, the CPU performance drops 97% for about 45 seconds. During that period, the CPU frequency has been down-clocked to 401~123MHz and the maximum reading of each thermal sensor drop from 81°C to 48°C.
Detailed log (CSV) and consolidated log (LibreOffice Calc) are available on GitHub.
Appendix
Tested on the following firmware configuration
BIOS 1.16 (N20ET31W) EC 1.05 (N20HT18W) ME 11.8.50.3460 (N20RG10W)