Laptop and CPU thermal throttling

I’ve been having some instability with my laptop recently and wondered if it might be heat related so I started to look into CPU speeds/throttling, it turned out to be an interesting topic. Almost all modern desktop and laptop CPUs have thermal based throttling, that is to say as the CPU starts to overheat it slows down. Let’s take my CPU as an example, an Intel Core i7 1165G7 in a Lenovo L14 Gen2. The CPU speed is ramped up and down based on needs with a base frequency of 2.8GHZ (to save power) and a turbo speed of 4.7GHZ. Actually seeing this throttling isn’t all that easy, hearing it is pretty easy as the fan starts to make more and more noise. Desktops are a lot better at heat management, they aren’t as compact and can move a LOT more air quietly.

To see throttling I tried a number of tools but the easiest one to visualize it is Open hardware monitor which is free. To see it you want to look at a graph of core temperature and CPU frequency. If you start to see a ledge where the CPUs are being capped, that’s what your looking for as an example of CPU throttling. The tool allows you to see a graph of them both.

Throttling starts as the CPU approaches it’s max temp of 100C. In this graph you can see two levels of throttling. First on the left you see it bringing the speed down from 4+GHZ down to around 3.8GHZ, and then a second throttling kicks in because the temperature did not come down enough and it slows the CPU down to the base 2.8GHZ which as you can see has an immediate and profound affect on the temperature.

In this second example you can see the CPU dropped even below the 2.8GHZ base speed all the way down below 2GHZ. Now while it’s great that the CPU is protected itself from melting down, the performance impact of this dramatic reduction in speed will be obvious. Now if your doing something like video editing this will be VERY important to find a way to limit.

Normally my laptop sits right on top of my desk, it pulls air from the underside of the laptop and blows it straight through the CPU and out. When sitting on the desk, or my lap for that matter the airflow is constrained. You can see the affect this has on the CPU temp in that the fan comes on sooner, and stays on longer, like 10 mins vs 3. Now a simple solution is to raise the laptop off the desk and make the airflow easier and this did absolutely help.

There is another way to see your CPU is being throttled. In task manager you will see that your CPU utilization from an OS point of view but the frequency of the CPU is not at max. In this case my CPU speed at 1.75GHZ Vs the max of 4.7GHZ.

As an interesting side note, while I could definitely see the CPU fan running longer, thus the CPU taking longer to cool, the time it took to export from Lightoom did not change measurably between on the desk and raised, which is curious to me.