linux-kernel - Re: [PATCH] thermal: cpufreq_cooling: freq_qos_update

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Date:   Wed, 17 Feb 2021 15:21:38 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Javi Merino <javi.merino@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amitk@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "v5 . 7+" <stable@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thermal: cpufreq_cooling: freq_qos_update_request()
 returns < 0 on error

On Wed, Feb 17, 2021 at 6:50 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> freq_qos_update_request() returns 1 if the effective constraint value
> has changed, 0 if the effective constraint value has not changed, or a
> negative error code on failures.
>
> The frequency constraints for CPUs can be set by different parts of the
> kernel. If the maximum frequency constraint set by other parts of the
> kernel are set at a lower value than the one corresponding to cooling
> state 0, then we will never be able to cool down the system as
> freq_qos_update_request() will keep on returning 0 and we will skip
> updating cpufreq_state and thermal pressure.
>
> Fix that by doing the updates even in the case where
> freq_qos_update_request() returns 0, as we have effectively set the
> constraint to a new value even if the consolidated value of the
> actual constraint is unchanged because of external factors.
>
> Cc: v5.7+ <stable@...r.kernel.org> # v5.7+
> Reported-by: Thara Gopinath <thara.gopinath@...aro.org>
> Fixes: f12e4f66ab6a ("thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping")
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
> Hi Guys,
>
> This needs to go in 5.12-rc.
>
> Thara, please give this a try and give your tested-by :).
>
>  drivers/thermal/cpufreq_cooling.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
> index f5af2571f9b7..10af3341e5ea 100644
> --- a/drivers/thermal/cpufreq_cooling.c
> +++ b/drivers/thermal/cpufreq_cooling.c
> @@ -485,7 +485,7 @@ static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
>         frequency = get_state_freq(cpufreq_cdev, state);
>
>         ret = freq_qos_update_request(&cpufreq_cdev->qos_req, frequency);
> -       if (ret > 0) {
> +       if (ret >= 0) {
>                 cpufreq_cdev->cpufreq_state = state;
>                 cpus = cpufreq_cdev->policy->cpus;
>                 max_capacity = arch_scale_cpu_capacity(cpumask_first(cpus));
> --
> 2.25.0.rc1.19.g042ed3e048af
>