linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Fix CPU lowest Frequency bug when offline/online for passive

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Date:   Mon, 13 Nov 2023 14:18:20 +0800
From:   Jinjie Ruan <ruanjinjie@...wei.com>
To:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
CC:     <zhaowenhui8@...wei.com>
Subject: Re: [PATCH] cpufreq: intel_pstate: Fix CPU lowest Frequency bug when
 offline/online for passive

Ping.

On 2023/11/7 10:58, Jinjie Ruan wrote:
> There is a bug in passive mode for intel pstate when
> CONFIG_X86_INTEL_PSTATE = y and configure intel_pstate = passive in command
> line. On Ice Lake server, although the performance tuner is used, the CPU
> have the lowest frequency in scaling_cur_freq after the CPU goes offline and
> then goes online, running the same infinite loop load.
> 
> How to reproduce:
> 
> cat while_true.c
> 	#include <stdio.h>
> 	void main(void)
> 	{
> 	        while(1);
> 	}
> 
> [root@...alhost freq_test]# cat test.sh
> 	#!/bin/bash
> 
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_governor
> 	taskset -c ${1} ./while_true &
> 	sleep 1s
> 
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> 	echo 0 > /sys/devices/system/cpu/cpu${1}/online
> 
> 	sleep 1s
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> 	sleep 1s
> 
> 	echo 1 > /sys/devices/system/cpu/cpu${1}/online
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> 	taskset -c ${1} ./while_true &
> 
> 	sleep 1s
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> 	sleep 1s
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> 	sleep 1s
> 	cat /sys/devices/system/cpu/cpu${1}/cpufreq/scaling_cur_freq
> 
> The CPU frequency is adjusted to the minimum after offline and online:
> 
> [root@...alhost freq_test]# sh test.sh 20
> 	2300000
> 	performance
> 	2299977
> 	cat: /sys/devices/system/cpu/cpu20/cpufreq/scaling_cur_freq: Device or
> 	resource busy
> 	800000
> 	800000
> 	800000
> 	799992
> [root@...alhost freq_test]# sh test.sh 21
> 	2300000
> 	performance
> 	2300000
> 	cat: /sys/devices/system/cpu/cpu21/cpufreq/scaling_cur_freq: Device or
> 	resource busy
> 	800000
> 	800000
> 	800000
> 	800000
> 
> As in __cpufreq_driver_target(), the cpufreq core will not call intel
> cpufreq's target() callback if the target freq is equal with policy->cur
> and do not set CPUFREQ_NEED_UPDATE_LIMITS flag, but the hardware also not
> proactively keep CPU with the policy->cur frequency. So also set
> CPUFREQ_NEED_UPDATE_LIMITS for passive mode. After applying this patch,
> the CPU frequency is consistent as what performance tuner expected after
> CPU offline and online as below:
> 
> [root@...alhost freq_test]# sh test.sh 20
> 	2300000
> 	performance
> 	2300000
> 	cat: /sys/devices/system/cpu/cpu20/cpufreq/scaling_cur_freq: Device or resource busy
> 	2300000
> 	2300000
> 	2299977
> 	2299977
> [root@...alhost freq_test]# sh test.sh 21
> 	2300000
> 	performance
> 	2300000
> 	cat: /sys/devices/system/cpu/cpu21/cpufreq/scaling_cur_freq: Device or resource busy
> 	2300000
> 	2300000
> 	2300000
> 	2300000
> [root@...alhost freq_test]# cat /sys/devices/system/cpu/intel_pstate/status
> 	passive
> 
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index a534a1f7f1ee..73403f1292b0 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -3091,7 +3091,7 @@ static int intel_cpufreq_suspend(struct cpufreq_policy *policy)
>  }
>  
>  static struct cpufreq_driver intel_cpufreq = {
> -	.flags		= CPUFREQ_CONST_LOOPS,
> +	.flags		= CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
>  	.verify		= intel_cpufreq_verify_policy,
>  	.target		= intel_cpufreq_target,
>  	.fast_switch	= intel_cpufreq_fast_switch,