linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Fix setting max_perf

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Message-ID: <2380747.QvGFG8o86Z@vostro.rjw.lan>
Date:	Thu, 16 Oct 2014 10:50:37 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pali Rohár <pali.rohar@...il.com>,
	'Dirk Brandewie' <dirk.j.brandewie@...el.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	'Dirk Brandewie' <dirk.brandewie@...il.com>
Subject: Re: [PATCH] cpufreq: intel_pstate: Fix setting max_perf_pct in performance policy

On Thursday, October 16, 2014 01:16:51 AM Pali Rohár wrote:
> Code which changes policy to powersave changes also max_policy_pct based on
> max_freq. Code which change max_perf_pct has upper limit base on value
> max_policy_pct. When policy is changing from powersave back to performance
> then max_policy_pct is not changed. Which means that changing max_perf_pct is
> not possible to high values if max_freq was too low in powersave policy.

Dirk, what do you think?

> Test case:
> 
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
> 800000
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> 3300000
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> performance
> $ cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 100
> 
> $ echo powersave > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> $ echo 800000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> $ echo 20 > /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> powersave
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> 800000
> $ cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 20
> 
> $ echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> $ echo 3300000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> $ echo 100 > /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> performance
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> 3300000
> $ cat /sys/devices/system/cpu/intel_pstate/max_perf_pct
> 24
> 
> And now intel_pstate driver allows to set maximal value for max_perf_pct based
> on max_policy_pct which is 24 for previous powersave max_freq 800000.
> 
> This patch will set default value for max_policy_pct when setting policy to
> performance so it will allow to set also max value for max_perf_pct.
> 
> Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> Cc: stable@...r.kernel.org
> ---
>  drivers/cpufreq/intel_pstate.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 0668b38..7547ab5 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -714,6 +714,7 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
>  	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
>  		limits.min_perf_pct = 100;
>  		limits.min_perf = int_tofp(1);
> +		limits.max_policy_pct = 100;
>  		limits.max_perf_pct = 100;
>  		limits.max_perf = int_tofp(1);
>  		limits.no_turbo = limits.turbo_disabled;
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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