linux-kernel - Re: [PATCH 3/4] PM / devfreq: Add cpu based scaling support to passive governor

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Message-ID: <YNItuDsinxDCVDGa@google.com>
Date:   Tue, 22 Jun 2021 11:36:40 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     andrew-sh.cheng@...iatek.com, hsinyi@...omium.org,
        sibis@...eaurora.org, saravanak@...gle.com,
        myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        chanwoo@...nel.org, cwchoi00@...il.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Saravana Kannan <skannan@...eaurora.org>
Subject: Re: [PATCH 3/4] PM / devfreq: Add cpu based scaling support to
 passive governor

On Thu, Jun 17, 2021 at 03:05:45PM +0900, Chanwoo Choi wrote:
> From: Saravana Kannan <skannan@...eaurora.org>
> 
> Many CPU architectures have caches that can scale independent of the
> CPUs. Frequency scaling of the caches is necessary to make sure that the
> cache is not a performance bottleneck that leads to poor performance and
> power. The same idea applies for RAM/DDR.
> 
> To achieve this, this patch adds support for cpu based scaling to the
> passive governor. This is accomplished by taking the current frequency
> of each CPU frequency domain and then adjust the frequency of the cache
> (or any devfreq device) based on the frequency of the CPUs. It listens
> to CPU frequency transition notifiers to keep itself up to date on the
> current CPU frequency.
> 
> To decide the frequency of the device, the governor does one of the
> following:
> * Derives the optimal devfreq device opp from required-opps property of
>   the parent cpu opp_table.
> 
> * Scales the device frequency in proportion to the CPU frequency. So, if
>   the CPUs are running at their max frequency, the device runs at its
>   max frequency. If the CPUs are running at their min frequency, the
>   device runs at its min frequency. It is interpolated for frequencies
>   in between.
> 
> Signed-off-by: Saravana Kannan <skannan@...eaurora.org>
> [Sibi: Integrated cpu-freqmap governor into passive_governor]
> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
> [Chanwoo: Fix conflict with latest code and clean code up]
> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
> ---
>  drivers/devfreq/governor.h         |  22 +++
>  drivers/devfreq/governor_passive.c | 264 ++++++++++++++++++++++++++++-
>  include/linux/devfreq.h            |  16 +-
>  3 files changed, 293 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
> index 9a9495f94ac6..3c36c92c89a9 100644
> --- a/drivers/devfreq/governor.h
> +++ b/drivers/devfreq/governor.h
> @@ -47,6 +47,28 @@
>  #define DEVFREQ_GOV_ATTR_POLLING_INTERVAL		BIT(0)
>  #define DEVFREQ_GOV_ATTR_TIMER				BIT(1)
>  
> +/**
> + * struct devfreq_cpu_data - Hold the per-cpu data
> + * @dev:	reference to cpu device.
> + * @first_cpu:	the cpumask of the first cpu of a policy.
> + * @opp_table:	reference to cpu opp table.
> + * @cur_freq:	the current frequency of the cpu.
> + * @min_freq:	the min frequency of the cpu.
> + * @max_freq:	the max frequency of the cpu.
> + *
> + * This structure stores the required cpu_data of a cpu.
> + * This is auto-populated by the governor.
> + */
> +struct devfreq_cpu_data {
> +	struct device *dev;
> +	unsigned int first_cpu;
> +
> +	struct opp_table *opp_table;
> +	unsigned int cur_freq;
> +	unsigned int min_freq;
> +	unsigned int max_freq;
> +};
> +
>  /**
>   * struct devfreq_governor - Devfreq policy governor
>   * @node:		list node - contains registered devfreq governors
> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> index fc09324a03e0..07e864509b7e 100644
> --- a/drivers/devfreq/governor_passive.c
> +++ b/drivers/devfreq/governor_passive.c
> @@ -8,11 +8,84 @@
>   */
>  
>  #include <linux/module.h>
> +#include <linux/cpu.h>
> +#include <linux/cpufreq.h>
> +#include <linux/cpumask.h>
> +#include <linux/slab.h>
>  #include <linux/device.h>
>  #include <linux/devfreq.h>
>  #include "governor.h"
>  
> -static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
> +#define HZ_PER_KHZ	1000
> +
> +static unsigned long get_taget_freq_by_required_opp(struct device *p_dev,
> +						struct opp_table *p_opp_table,
> +						struct opp_table *opp_table,
> +						unsigned long freq)
> +{

s/get_taget_freq_by_required_opp/get_target_freq_by_required_opp/