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

Doug Smythies
2024-02-09T21:38:13Z

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@mail.gmail.com/