2.2 GHz (Turbo Boost使用時最大3.4 GHz), 2.5 GHz (Turbo Boost使用時最大3.7 GHz)もしくは2.8 GHz (Turbo Boost使用時最大4.0 GHz) L3キャッシュで6 MBのクアッドコアIntel Core i7プロセッサ

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kernel_task takes up 500% of my CPU when plugging in external monitor

Since I plugged in an external monitor (via thunderbolt) my kernel_task ramps up to 500% and can’t do much on my MBP.

I researched a lot online and did the following:

  • Disabled Energy Saver - Automatic Graphics Switching on both Battery and Power Adapter mode
  • Disabled Spotlight indexing for specific types of content and also added folders like “/System” in the Privacy settings
  • Reset the System Management Controller (SMC)
  • Performed the Apple Diagnostics test (ADT - some older websites called it the Apple Hardware Test - AHT) and had no issues come from that.
  • I also use Google Drive’s “Backup and Sync” and do lots of web development with `node_modules` folders, that can have 10s of thousands of small files which I think results in CPU churn. I’ve disabled it now.
  • Shut down the computer and turned it back on. Still get same issues with the external monitor.

Now with no external monitor plugged in, every once and a while the kernel_task rises up to 300% and sometimes rarely to 500%. I’m curious if it is a software thing or a hardware thing. To me it seems more like a software thing.

I use VS Code for programming which can have a lot of background tasks, same with using node/npm which can probably be doing lots in the background. I also run iStat v6.30, and sadly I have only 21 GB of free space on my HDD (out of 500 GB…). Often I also have Slack open, and I know that’s a web app using Electron to run as a desktop application, which can be notorious for performance.

Often the fans can run high as well. I often suspect it is either due to the VS Code/npm/node/Slack thing, or kernel_task, or maybe something else I’m unaware about.

When checking memory usage via iStat, I can see that kernel_task is using 1.61 GB (oof, Firefox is using 6.36 GB).

Things I haven’t tried yet:

  • Cleaning out more free space from HDD
  • Using plain HDMI cable into the HDMI cable port
  • Taking MBP apart and cleaning any potential dust

Has anyone had similar experience with this issue and how to address it?

OS: 10.13.6

Processor: 2.5 GHz Intel Core i7

Memory: 16 GB 1600 MHz DDR3

Graphics: AMD Radeon R9 M370X 2048 MB, Intel Iris Pro 1536 MB

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The Thunderbolt to HDMI adapter you are using has damaged your Thunderbolt port.

Also check your AC power outlets and the monitor/TV is plugged in to the same outlet and the polarized plug is plugged in correctly. Its possible you zapped your port by cross-wired AC between your system and display so the ground side was hot!

Get a outlet checker to check the outlets.


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Matt Scheurich さん、ありがとうございました!

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