Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency invariance

On 6/25/2021 10:37 AM, Ionela Voinescu wrote:

Quick questions for you:

1. When you say you tried a 5.4 kernel, did you try it with these
patches backported? They also have some dependencies with the recent
changes in the arch topology driver and cpufreq so they would not be
straight forward to backport.

If the 5.4 kernel you tried did not have these patches, it might be best
to try next/master that has these patches, but with
CONFIG_ACPI_CPPC_CPUFREQ_FIE=n, just to eliminate the possibility that
an incorrect frequency scale factor here would affect utilization that
would then affect the schedutil frequency selection. I would not expect
this behavior even if the scale factor was wrong, but it would be good
to rule out.

2. Is your platform booting with all CPUs? Are any hotplug operations
done in your scenario?

Ionela, I found that set ACPI_PROCESSOR=y instead of ACPI_PROCESSOR=m will fix the previous mentioned issues here (any explanations of that?) even though the scaling down is not perfect. Now, we have the following on this idle system:

# cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
 	79 1000000
  	1 1160000
 	73 1400000
  	1 2000000
  	4 2010000
  	1 2800000
  	1 860000

Even if I rerun a few times, there could still have a few CPUs running lower than lowest_perf (1GHz). Also, even though I set all CPUs to use "userspace" governor and set freq to the lowest. A few CPUs keep changing at will.

# cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
	156 1000000
  	3 2000000
  	1 760000