![]() Outputting to only one monitor (the count includes the built-in monitor), with no scaling or integer scaling of the resolution, seems to reduce the power usage to ~9W and thus mostly solve the issue.įrom the sensor data, it seems that the trigger for the throttling were most likely the Thunderbolt Left/Right Proximity temperatures. ![]() This quickly leads to the chassis overheating. which would probably not be practical for most people.Īn AMD Community thread further pointed out that the culprit is that the dGPU goes on full drive and draws ~20W of power whenever the laptop outputs to multiple monitors, seemingly because the driver lets the dGPU memory run on full clock speed "to avoid tearing". The ultimate solution seems to be to use an eGPU. If you're encountering this on Macbook Pro 16" (2019), this seems to be a well-known problem regarding the laptop body not being able to handle the heat from both the CPU and GPU when external monitors are connected. Of course that leads to false conclusions more often than not. Otherwise guessing and testing is the only way. You can then examine stack traces and guess what they mean. That means getting a debug kernel from Apple, rebooting, then using a second Mac to attach to the debugged machine. The only way to actually ask the kernel what it's doing is to attach a kernel debugger. How can I find out what this process is doing? No kernel_task either, but the machine becomes unusable from something throttling.Įrgo, high CPU usage by kernel_task is caused by high Thunderbolt Left Proximity temperature, which is caused by charging and having normal peripherals plugged in at the same time. Plugging everything into the two right ports instead of the left raised the Right temperatures to over 100 degrees, without the fans coming on. Note that high temperature on the right side appears to be ignored by the OS. (all other temperatures were both low and flat. Both the hub (mouse and keyboard ONLY) and HDMI adapter individually raise the temperature about 10 degrees, and 15 degrees together. State C shows that simply having stuff plugged in to TB ports raises their temperature significantly. Again moving power back to the right side, restoring State B, resolves the problem immediately. Moving power back to the left side, restoring State A, quickly restores the temperatures and kernel_task again comes back after 3-4 minutes. The left side temperature drops and the kernel_task goes away within about 15 seconds. ![]() State B cures the kernel_task problem by moving power from the left ports to the right. About 3-4 minutes later the dreaded kernel_task high CPU usage starts. You can see the Thunderbolt Left Proximity temperature sensor rise quickly. State A a USB-C hub (a mouse and keyboard, plus power) and a USB-C HDMI 2.0 adapter, both on the left side. The machine had been used on battery then plugged in. A hot CPU is throttled by reducing its clock speed, not by scheduling fake no-op load. ![]() ![]() Some MBP (eg 15" Intel touchbar models) have a design quirk where this config can get hotter than it should.Īctual CPU temperature or application CPU usage is uncorrelated with kernel_task. If using both laptop display and external display try switching to just one or the other (I switched to external only, laptop lid closed).iStatMenus has an easy Sensors -> Fans menu item to do so. Either power or another accessory until the battery is full. Avoid plugging everything on the right side (see last paragraph below). If you have a second charger then plug it in on the right side. Move charging from the left to the right side.In particular Left Thunderbolt port usage. High kernel_task CPU Usage is due to high chassis temperature caused by charging. TLDR If your MacBook Pro runs hot or shows a high % CPU for the kernel task, try charging on the right and not on the left. ![]()
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