very simple: add 'cpu load monitor' or 'network monitor' or 'memory status' to the desktop. No need to resize or reposition, just wait a few seconds. The CPU load of the system goes up to 100% (other widgets do not show this behaviour) Reproducible: Always
Well, *I confirm that*, and add one more: The Instant messaging "notification widget" can also use a 100% of one CPU core: if you add an account with a wrong password, it tries to reconnect and that start the "connecting" circle animation consumming 100% of one core. I think that when someone messages you, the envelop animation can also consume a lot of CPU.
Worth to say that I switched off the IM checkbox at the systray preferences and CPU restores to its tipical use. If you switch on again, you'll have the plasmashell consumming 100% of CPU again.
Maybe duplicate: bug 345696 Maybe related: bug 352813 bug 359890 bug 364061
high CPU Thanks, but this isn't very helpful on it's own, so I'm going to close this, but please see the linked reports. We have multiple high CPU bugs, some caused by us, some not, some fixed, some unknown. It's hard to say what the cause of each one is, and bug reports get convuluted. I've made a list of some of the bigger more specific ones: For high CPU caused by reloading icons over the SNI protocols see: 356479 For high CPU caused by infinite spurious X events see: 373368 For others, search other bug reports here.