sched/cpufreq: Rework schedutil governor performance estimation - Regression bisected

[Doug Smythies]

Hi,

I noticed a regression in the 6.8rc series kernels. Bisecting the kernel pointed to:

# first bad commit: [9c0b4bb7f6303c9c4e2e34984c46f5a86478f84d]
sched/cpufreq: Rework schedutil governor performance estimation

There was previous bisection and suggestion of reversion,
but I guess it wasn't done in the end. [1]

The regression: reduced maximum CPU frequency is ignored.

Conditions:
CPU frequency scaling driver: intel_cpufreq (a.k.a intel_pstate in passive mode)
CPU frequency scaling governor: schedutil
HWP (HardWare Pstate) control (a.k.a. Intel_speedshift): Enabled
Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz

I did not check any other conditions, i.e. HWP disabled or the acpi-cpufreq driver.

Example: A 100% load on CPU 5.

sudo turbostat --quiet --Summary --show Busy%,Bzy_MHz,IRQ,PkgWatt,PkgTmp,RAMWatt,GFXWatt,CorWatt --interval 15
Busy%   Bzy_MHz IRQ     PkgTmp  PkgWatt CorWatt GFXWatt RAMWatt
8.42    4636    21823   67      28.40   27.56   0.00    2.59
8.40    4577    17724   66      27.57   26.73   0.00    2.59
8.35    4637    19535   66      28.65   27.81   0.00    2.60
8.41    4578    20723   66      27.73   26.89   0.00    2.59
8.40    4558    19156   67      27.39   26.55   0.00    2.58
8.34    4502    18127   67      26.79   25.96   0.00    2.57

grep . /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu10/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu11/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu1/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu2/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu3/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu4/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu5/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu6/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu7/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu8/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu9/cpufreq/scaling_max_freq:2400000

grep . /sys/devices/system/cpu/cpu5/cpufreq/*
/sys/devices/system/cpu/cpu5/cpufreq/affected_cpus:5
/sys/devices/system/cpu/cpu5/cpufreq/base_frequency:4100000
/sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_max_freq:4800000
/sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_min_freq:800000
/sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_transition_latency:20000
/sys/devices/system/cpu/cpu5/cpufreq/energy_performance_available_preferences:default performance balance_performance balance_power
power
/sys/devices/system/cpu/cpu5/cpufreq/energy_performance_preference:balance_performance
/sys/devices/system/cpu/cpu5/cpufreq/related_cpus:5
/sys/devices/system/cpu/cpu5/cpufreq/scaling_available_governors:conservative ondemand userspace powersave performance schedutil
/sys/devices/system/cpu/cpu5/cpufreq/scaling_cur_freq:4799998
/sys/devices/system/cpu/cpu5/cpufreq/scaling_driver:intel_cpufreq
/sys/devices/system/cpu/cpu5/cpufreq/scaling_governor:schedutil
/sys/devices/system/cpu/cpu5/cpufreq/scaling_max_freq:2400000
/sys/devices/system/cpu/cpu5/cpufreq/scaling_min_freq:800000
/sys/devices/system/cpu/cpu5/cpufreq/scaling_setspeed:<unsupported>

[1] https://lore.kernel.org/all/CAKfTPtDCQuJjpi6=zjeWPcLeP+ZY5Dw7XDrZ-LpXqEAAUbXLhA@xxxxxxxxxxxxxx/