[collectd 6] cpufreq plugin: migration to collectd 6.

[octo]

ChangeLog: cpufreq plugin: Migration to v6.0. Support for the "cpufreq-stats" Linux driver has been dropped because the code was hard to port and had no test coverage.

[eero-t]

Time-in-state stats are not enabled by default in kernel, and not available for CPUs which frequency / power management is done by firmware (instead of kernel being in control of changing the frequencies by itself): https://www.kernel.org/doc/Documentation/cpu-freq/cpufreq-stats.txt

=> dropping that info is OK'ish.

However, Changelog entry should mention that time-in-state info is dropped, as that's the actually useful information, whereas scaling frequency value is just a sample of a value that can fluctuate between its min & max values at few millisecond intervals (i.e. basically a random value for anything else than steady-state workloads)...

[octo]

Reworded the ChangeLog entry. I agree that the time-in-state info is much more meaningful than the point-in-time information. I'll see if I can find the cpufreq-stats kernel module on my development machine.

[eero-t]

For unit tests, you could change plugin code to take prefix for the sysfs stats directory, and point the code to a directory with fake time-in-state files (which content could be e.g. copied from the linked kernel doc).

Those files could be either generated at run-time to randomized dir, or pre-created e.g. under src/test-files/cpufreq/{stats1,stats2,invalid}/.