linux-kernel - Re: sched/cpufreq: Rework schedutil governor performance estimation

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Date: Fri, 9 Feb 2024 23:10:40 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Doug Smythies <dsmythies@...us.net>
Cc: Ingo Molnar <mingo@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: sched/cpufreq: Rework schedutil governor performance estimation -
 Regression bisected

On Fri, 9 Feb 2024 at 22:38, Doug Smythies <dsmythies@...us.net> wrote:
>
> 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]

This has been fixed with
https://lore.kernel.org/all/170539970061.398.16662091173685476681.tip-bot2@tip-bot2/

>
> The regression: reduced maximum CPU frequency is ignored.

This seems to be something new.
schedutil doesn't impact the max_freq and it's up to cpufreq driver
select the final freq which should stay within the limits

>
> 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/
>
>