Created attachment 279350 [details]
Screenshots: Before deactivating a CPU, after deactivatiing a CPU, after restarting system monitor. Output of the "top" command for comparison.

In the resources tab, if a CPU in a multi-CPU system is taken offline (by setting the value in the file /sys/devices/system/cpu/cpu?/online to 0), the system monitor will report a zero load for all CPUs following the offline CPU. For example, if you deactivate CPU5 in a system with 8 CPUs, the CPUs 5-7 will show 0% load. This is incorrect, as can be seen with other CPU monitors (for example "top"). Furthermore, if you restart the system monitor, it will only show CPUs up to the first offline-CPU. In the example above, it would only show CPUs 0-4.

Steps to reproduce:
-Have a multi-CPU system :-)
-Generate load for all CPUs, for example using the "stress" tool
-Open system monitor
-Deactivate a CPU: "echo 0 | sudo tee /sys/devices/system/cpu/cpuX/online", replacing "X" with an appropriate number

Expected result:
System monitor still shows load for all CPUs != X

Actual result:
System monitor only reports load for CPUs < X

See attached screenshots.