Building A Macos App To Know When My Mac Is Thermal Throttling

I’ve been very happy with my M2 MacBook Air for the past few years. However, when using an external display, especially a very demanding one like a 4K 120Hz display, I’ve noticed it started struggling more. Since it lacks fans, you can’t hear it struggling, but you can feel it as everything becomes very slow or unresponsive: that’s when thermal throttling kicks in.

I know it’s thermal throttling because I can see in iStat Menus that my CPU usage is 100% while the power usage in watts goes down.

It’s even more obvious with MX Power Gadget: You can see the power usage and frequency of the performance core dropping, as usage keeps being 100%:

I’ve also hit thermal throttling with my work MacBook Pro. It’s the 14" M4 Max variant, which is the worst variant because the thermal envelope of the 14" is too small for the max output for the M4 Max. On my previous 14" M1 Pro MacBook Pro, I’ve never even heard the fans in 3 years…

That being said, I still love Apple Silicon for the performance and power usage, it’s still a dramatic improvement over the Intel days. 🫶

Anyway, I wanted to know: is there a way to tell if the Apple Silicon SoC is thermal throttling, that is not based on heuristics like in my screenshot?

This was a wilder ride than I expected. It’s possible to know programmatically if the Mac is throttled, because macOS exposes this in various but inconsistent ways.

The approach that Apple recommends is to use ProcessInfo.thermalState from Foundation:

Sounds good, right? However, I knew that another tool could provide this information, though it needed root: powermetrics.

Both report the pressure level to be “nominal”, they must be the same…right?

Source: HackerNews