linux: fix cpu_freq() when one cpufreq policy affects multiple CPUs

[justeph]

Summary

• OS: Ubuntu
• Bug fix: yes
• Type: core
• Partially fixes [Debian unstable] 3 tests failing on several "uncommon" architectures #2557

Description

Some platforms (like RISC-V) only expose one cpufreq policy that manages multiple CPUs. This breaks psutil's assumption that each CPU has its own policy directory.

This patch reads affected_cpus for each policy and maps CPUs to the correct policy path.

For example on my bananapif3, I have:

root@bananapif3:~# cat /sys/devices/system/cpu/cpufreq/policy0/related_cpus 
0 1 2 3 4 5 6 7
root@bananapif3:~# ls /sys/devices/system/cpu/cpufreq/
boost policy0
root@bananapif3:~# cat /proc/cpuinfo  | grep processor | wc -l 
8

without the path, I have:

>>> import psutil
>>> psutil.cpu_freq(percpu=True)
[scpufreq(current=1600.0, min=614.4, max=1600.0)]
>>> psutil.cpu_count()
8

with the patch:

>>> import psutil
>>> psutil.cpu_freq(percpu=True)
[scpufreq(current=1600.0, min=614.4, max=1600.0), scpufreq(current=1600.0, min=614.4, max=1600.0), cpufreq(current=1600.0, min=614.4, max=1600.0), scpufreq(current=1600.0, min=614.4, max=1600.0), scpufreq(current=1600.0, min=614.4, ax=1600.0), scpufreq(current=1600.0, min=614.4, max=1600.0), scpufreq(current=1600.0, min=614.4, max=1600.0), cpufreq(current=1600.0, min=614.4, max=1600.0)]
>>> len(psutil.cpu_freq(percpu=True))
8
>>> psutil.cpu_count()
8

[justeph]

Hi @giampaolo, I don't think the 2 errors from CI are related to my changes. Is there any thing I can do?