High CPU usage when updating top bar

This test case is for gnome 3.34.2 on fedora 31, intel coffee lake CPU with builtin GPU (all extensions are off).

1. In gnome tweak tool, turn on Top Bar->Seconds slider to have regular updates to the top bar (show clock seconds).

• The CPU usage and power consumption goes up considerably.

3. Wait for screen to go blank (sleep)

• Observe another big step up in power consumption.
• Logging in with ssh, one can see gnome-shell process using unusually high CPU.

This behaviour can also be triggered by other extensions regularly updating the top bar panel, i.e. sensors data. Sometimes this even causes the system to reboot shortly after the monitor screen goes blank.