Are You Charging Your MacBook the Wrong Way?

Yes, you read the title correctly. There are obviously “right” and “wrong” ways to connect devices to a MacBook with Thunderbolt / USB-C ports on both sides. Incorrect execution can affect the performance of your computer.

I recently came across this knowledge on a thread on StackExchange , and I was surprised to find that there can be a significant difference in the stability of your system depending on how you charge and connect devices to your MacBook – MacBook Pro, in this example. The decision to put everything on one side can affect how hot your system gets, and a hotter system is more likely to see its CPU throttled to lower its internal temperature, resulting in decreased performance.

Before I get to that, I want to point out that I said which side you choose to charge from can make a difference; I am not sure if this is a universal problem for all MacBooks and it is not the only problem that could be causing your system. slow down. However, this is an unusual troubleshooting technique that most people would never think of, so it’s worth knowing about.

First, let’s look at the original problem that led to this discovery, just to keep us all on the same page. As StackExchange user Adam wrote:

Sometimes my machine will have an instance of kernel_task maximum CPU kernel_task :. This can take anywhere from a few minutes to hours. In this state, the machine is practically unusable. Rebooting doesn’t help; the new kernel_task appears again until it completes whatever it is doing.

How can I know what this process is doing?

StackExchange user BMike responded with an excellent description of how multiple devices plugged into the left side of your MacBook Pro can affect the internal temperature of your system – mostly if you have devices plugged in and charging your MacBook Pro from the same side. You can skip to the answer to see the various graphs BMike has generated to track CPU usage in various “whats connected and where” scenarios, but here’s an overview:

Actual CPU temperature or application CPU usage does not correlate with kernel_task . A “hot” CPU is throttled by reducing its clock speed rather than scheduling a false idle load.

The graphs below are taken from iStatMenus. The machine was running on battery power and then plugged into a power outlet.

On the left side are a USB-C hub (mouse and keyboard, plus power) and a USB-C HDMI 2.0 adapter. You can see the Thunderbolt Left Proximity temperature sensor go up quickly. After about 3-4 minutes the kernel_task processor kernel_task .

State B kernel_task issue kernel_task , moving power from left ports to right ports. The left side temperature drops and kernel_task disappears after about 15 seconds.

This is causal. Moving the power back to the left, restoring state A, quickly restores the temperature, and kernel_task returns again after 3-4 minutes. Moving the power back to the right side again, restoring state B immediately resolves the problem.

State C indicates that simply plugging into the TB ports will significantly increase their temperature. Both the hub (mouse and keyboard ONLY) and the HDMI adapter separately increase the temperature by about 10 degrees and 15 degrees together.

So what’s the bottom line? If you find that your MacBook stops working, check Activity Monitor to see if you can find an obvious cause. If you notice a not-so-descriptive process that ties up your system’s resources — for example, “kernel_task” — take a moment to see what you’ve connected to your laptop and where.

If you are using all the ports on the left side to charge your MacBook and connect other devices, try sharing the load: for example, moving the charging cable to the right side is all you need to do. reduce the performance throttling you experience. Likewise, resist the urge to just move everything to the right side – you may not experience the same suffocation, but you may still face some system instability.

In short: if possible, divide the difference. And if you can’t – because you just need to connect so much hardware to your MacBook Pro, explore alternative cooling scenarios. While it looks silly, a third-party cooling pad might be all you need to keep your warm MacBook running smoothly.

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