linux-kernel - Re: [RFC/RFT][PATCH 1/2] cpufreq: schedutil: Use policy-dependent transition delays

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Date:   Sat, 15 Apr 2017 00:51:56 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PM <linux-pm@...r.kernel.org>
Cc:     Juri Lelli <juri.lelli@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Joel Fernandes <joelaf@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Brendan Jackman <brendan.jackman@....com>
Subject: Re: [RFC/RFT][PATCH 1/2] cpufreq: schedutil: Use policy-dependent transition delays

On Tuesday, April 11, 2017 12:20:41 AM Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Make the schedutil governor take the initial (default) value of the
> rate_limit_us sysfs attribute from the (new) transition_delay_us
> policy parameter (to be set by the scaling driver).
> 
> That will allow scaling drivers to make schedutil use smaller default
> values of rate_limit_us and reduce the default average time interval
> between consecutive frequency changes.
> 
> Make intel_pstate set transition_delay_us to 500.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> This is a replacement for https://patchwork.kernel.org/patch/9671831/

Any concerns about this one?

> 
> ---
>  drivers/cpufreq/intel_pstate.c   |    2 ++
>  include/linux/cpufreq.h          |    7 +++++++
>  kernel/sched/cpufreq_schedutil.c |   15 ++++++++++-----
>  3 files changed, 19 insertions(+), 5 deletions(-)
> 
> Index: linux-pm/include/linux/cpufreq.h
> ===================================================================
> --- linux-pm.orig/include/linux/cpufreq.h
> +++ linux-pm/include/linux/cpufreq.h
> @@ -120,6 +120,13 @@ struct cpufreq_policy {
>  	bool			fast_switch_possible;
>  	bool			fast_switch_enabled;
>  
> +	/*
> +	 * Preferred average time interval between consecutive invocations of
> +	 * the driver to set the frequency for this policy.  To be set by the
> +	 * scaling driver (0, which is the default, means no preference).
> +	 */
> +	unsigned int		transition_delay_us;
> +
>  	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
>  	unsigned int cached_target_freq;
>  	int cached_resolved_idx;
> Index: linux-pm/kernel/sched/cpufreq_schedutil.c
> ===================================================================
> --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
> +++ linux-pm/kernel/sched/cpufreq_schedutil.c
> @@ -491,7 +491,6 @@ static int sugov_init(struct cpufreq_pol
>  {
>  	struct sugov_policy *sg_policy;
>  	struct sugov_tunables *tunables;
> -	unsigned int lat;
>  	int ret = 0;
>  
>  	/* State should be equivalent to EXIT */
> @@ -530,10 +529,16 @@ static int sugov_init(struct cpufreq_pol
>  		goto stop_kthread;
>  	}
>  
> -	tunables->rate_limit_us = LATENCY_MULTIPLIER;
> -	lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
> -	if (lat)
> -		tunables->rate_limit_us *= lat;
> +	if (policy->transition_delay_us) {
> +		tunables->rate_limit_us = policy->transition_delay_us;
> +	} else {
> +		unsigned int lat;
> +
> +		tunables->rate_limit_us = LATENCY_MULTIPLIER;
> +		lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
> +		if (lat)
> +			tunables->rate_limit_us *= lat;
> +	}
>  
>  	policy->governor_data = sg_policy;
>  	sg_policy->tunables = tunables;
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -41,6 +41,7 @@
>  #define INTEL_PSTATE_HWP_SAMPLING_INTERVAL	(50 * NSEC_PER_MSEC)
>  
>  #define INTEL_CPUFREQ_TRANSITION_LATENCY	20000
> +#define INTEL_CPUFREQ_TRANSITION_DELAY		500
>  
>  #ifdef CONFIG_ACPI
>  #include <acpi/processor.h>
> @@ -2237,6 +2238,7 @@ static int intel_cpufreq_cpu_init(struct
>  		return ret;
>  
>  	policy->cpuinfo.transition_latency = INTEL_CPUFREQ_TRANSITION_LATENCY;
> +	policy->transition_delay_us = INTEL_CPUFREQ_TRANSITION_DELAY;
>  	/* This reflects the intel_pstate_get_cpu_pstates() setting. */
>  	policy->cur = policy->cpuinfo.min_freq;
>  
>