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Today I learned something again. My MacBook Pro suddenly became quite slow, keystrokes took seconds and the mouse pointer only moved in slow motion. A look at the "Activity Monitor" utility - permanently installed in macOS and to be found under "Applications" -> "Utilities" - immediately showed me the cause: A process called "VTDecoderXPCService" has the CPU heavily besieged and almost continuously over 100% of the computing time drawn.
What is the process doing?
A quick research on the Apple Support forums showed me that I seemingly not the only one am where the process surfaced. Apple's rationale is as follows:
The VTDecoderXPCService process is responsible for all sorts of things that come with Quicktime related. It "sandboxes" these processes and ensures that they cannot access unwanted memory areas. So if audio or video playback is involved in any way, then the process on macOS Sierra is likely to be involved.
In my case, it was almost clear to me which program was responsible for this, because further down I found the process "com.apple.photos.VideoConversionService" and this - so I assumed - downsizes the videos from my photo library, to upload them to iCloud. I closed "Photos" as a test and the Mac promptly ran again without snail mode.
Troubleshooting with activity monitor and program switcher
However, according to the Apple support forums, a webcam, video display, or similar can also trigger the process. So you should think about what is running on your Mac that might have called this process. Terminating programs at a time interval helps to check which program could be responsible. You can see which programs are running by pressing "cmd" + Tab on the keyboard.
What does the kernel_task process do?
If you are wondering what the top process in the screenshot called "kernel_task" is doing, which also generates over 100% CPU load here: This process intervenes when the Mac's CPU gets too hot. Then the processes are interrupted and only processed piecemeal so that the CPU can cool down. The result is that the Mac becomes very slow. If you provide better ventilation and cooling, the CPU load of the kernel_task process drops again.
By the way, I can recommend the "iStat Menus" program to keep an eye on the CPU load and the temperature of the CPU. With this you can show a small graph and the current temperature of the CPU in the menu bar, which is very practical.
Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.
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