Linux: skip offline cpu cores in cpu_freq

[shadeyg56]

Summary

Fixes #2254

Previously offline CPU cores would return an error in cpu_freq() since psutil didn't skip them. With this change, any CPU core found to be offline will return scpufreq(0, 0, 0) I figured it would be pretty common for programs to expect the cores to be returned in order which is why I had it append a tuple with all-zero values. If this is unwanted, it could be easily removed to only return online cpus and their frequencies.

• OS: Linux
• Bug fix: yes
• Type: core
• Fixes: #2254

Description

Runs cat on /sys/devices/system/cpu/cpu{i}/online to determine if a CPU is offline or not. If cat returns 0, then scpufreq(0, 0, 0) is appended and the loop continues to the next iteration. Otherwise, the function runs as normal.

[giampaolo]

Nice. Some remarks:

• I'd rather put the new logic in here, after if curr is None, and raise NotImplementedError if also the new file is unreadable.
• the 0 value should be a float (0.0)
• if you can, also update HISTORY.rst / CREDITS files

Thank you

[shadeyg56]

Do I need to remove the f-string in order to support python 2?

[giampaolo]

Oh right. Yes.