How can I find and reduce unexpectedly high CPU usage on Linux Mint?
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MellowPine47
I'm running Linux Mint 22.3 on an older MacBook Pro with an Intel i5 and 16 GB of RAM. I moved to Linux because macOS had become sluggish, and Mint initially felt much faster. Recently, though, all four CPU cores often reach 100% during ordinary tasks such as browsing with around ten tabs and having a few applications open. Firefox sometimes uses between 25% and 90% CPU, Cinnamon appears to use roughly 25%, and Thunderbird can also spike. I'd like to determine what is actually consuming the CPU and whether overheating, browser extensions, hardware acceleration, or another configuration problem could be responsible. What steps can I take to diagnose and improve the performance?
Answers
Start by watching System Monitor or running `htop` while the slowdown is happening. Sort by CPU usage and check whether Firefox, Thunderbird, Cinnamon, or a background process is responsible. Try Firefox in troubleshooting mode or temporarily disable extensions to see whether one of them is causing the spikes. Also test whether the CPU stays busy when Firefox is closed; that helps separate a browser problem from a system-wide one.
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High CPU usage isn’t automatically a Mint optimization problem—the important question is which process is using it and whether that usage is expected. Ten browser tabs, extensions, video pages, and background Thunderbird indexing can add up on an older mobile i5. Compare Firefox with a clean profile or another browser, but don’t assume switching browsers will fix it until you identify the workload causing the spikes.
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If the usage is high even when you aren’t doing much, check temperatures and clock speed. An aging MacBook can collect dust or have a failing thermal system, causing the processor to overheat and reduce its clock speed. Tools such as `lm-sensors` can help inspect temperatures. In `htop`, also look for processes doing software rendering or video decoding instead of using the GPU, especially when playing browser videos.
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MellowPine47: Firefox is usually the biggest user, sometimes jumping between 25% and 90%, while Cinnamon sits around 25% and Thunderbird can spike too. I’ll test with extensions disabled and check the temperatures before deciding whether to switch browsers.