linux-kernel - Re: [PATCH v2 1/4] cpufreq: Introduce CPUFREQ_NEED_UPDATE

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Date:   Tue, 27 Oct 2020 08:36:15 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH v2 1/4] cpufreq: Introduce CPUFREQ_NEED_UPDATE_LIMITS
 driver flag

On 23-10-20, 17:35, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Generally, a cpufreq driver may need to update some internal upper
> and lower frequency boundaries on policy max and min changes,
> respectively, but currently this does not work if the target
> frequency does not change along with the policy limit.
> 
> Namely, if the target frequency does not change along with the
> policy min or max, the "target_freq == policy->cur" check in
> __cpufreq_driver_target() prevents driver callbacks from being
> invoked and they do not even have a chance to update the
> corresponding internal boundary.
> 
> This particularly affects the "powersave" and "performance"
> governors that always set the target frequency to one of the
> policy limits and it never changes when the other limit is updated.
> 
> To allow cpufreq the drivers needing to update internal frequency
> boundaries on policy limits changes to avoid this issue, introduce
> a new driver flag, CPUFREQ_NEED_UPDATE_LIMITS, that (when set) will
> neutralize the check mentioned above.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> New patch in v2.
> 
> ---
>  drivers/cpufreq/cpufreq.c |    3 ++-
>  include/linux/cpufreq.h   |   10 +++++++++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> Index: linux-pm/include/linux/cpufreq.h
> ===================================================================
> --- linux-pm.orig/include/linux/cpufreq.h
> +++ linux-pm/include/linux/cpufreq.h
> @@ -297,7 +297,7 @@ __ATTR(_name, 0644, show_##_name, store_
>  
>  struct cpufreq_driver {
>  	char		name[CPUFREQ_NAME_LEN];
> -	u8		flags;
> +	u16		flags;
>  	void		*driver_data;
>  
>  	/* needed by all drivers */
> @@ -417,6 +417,14 @@ struct cpufreq_driver {
>   */
>  #define CPUFREQ_IS_COOLING_DEV			BIT(7)
>  
> +/*
> + * Set by drivers that need to update internale upper and lower boundaries along
> + * with the target frequency and so the core and governors should also invoke
> + * the diver if the target frequency does not change, but the policy min or max
> + * may have changed.
> + */
> +#define CPUFREQ_NEED_UPDATE_LIMITS		BIT(8)
> +
>  int cpufreq_register_driver(struct cpufreq_driver *driver_data);
>  int cpufreq_unregister_driver(struct cpufreq_driver *driver_data);
>  
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -2191,7 +2191,8 @@ int __cpufreq_driver_target(struct cpufr
>  	 * exactly same freq is called again and so we can save on few function
>  	 * calls.
>  	 */
> -	if (target_freq == policy->cur)
> +	if (target_freq == policy->cur &&
> +	    !(cpufreq_driver->flags & CPUFREQ_NEED_UPDATE_LIMITS))

I was wondering if the same change should be made in the target_index part as we
do this kind of check again ? But then I thought that since we know there are no
users of that right now, why bother :)

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh