linux-kernel - RE: [PATCH] cpufreq: schedutil: Don't skip freq update when limits change

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Message-ID: <001201d54125$a6a82350$f3f869f0$@net>
Date:   Tue, 23 Jul 2019 00:10:01 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Viresh Kumar'" <viresh.kumar@...aro.org>,
        "'Rafael Wysocki'" <rjw@...ysocki.net>,
        "'Ingo Molnar'" <mingo@...hat.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>
Cc:     <linux-pm@...r.kernel.org>,
        "'Vincent Guittot'" <vincent.guittot@...aro.org>,
        <joel@...lfernandes.org>, "'v4 . 18+'" <stable@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] cpufreq: schedutil: Don't skip freq update when limits change

On 2019.07.21 23:52 Viresh Kumar wrote:

> To avoid reducing the frequency of a CPU prematurely, we skip reducing
> the frequency if the CPU had been busy recently.
> 
> This should not be done when the limits of the policy are changed, for
> example due to thermal throttling. We should always get the frequency
> within limits as soon as possible.
>
> Fixes: ecd288429126 ("cpufreq: schedutil: Don't set next_freq to UINT_MAX")
> Cc: v4.18+ <stable@...r.kernel.org> # v4.18+
> Reported-by: Doug Smythies <doug.smythies@...il.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> @Doug: Please try this patch, it must fix the issue you reported.

It fixes the driver = acpi-cpufreq ; governor = schedutil test case
It does not fix the driver = intel_cpufreq ; governor = schedutil test case

I have checked my results twice, but will check again in the day or two.

... Doug

>
> kernel/sched/cpufreq_schedutil.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 636ca6f88c8e..b53c4f02b0f1 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -447,7 +447,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>  	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> 	unsigned long util, max;
>  	unsigned int next_f;
> -	bool busy;
> +	bool busy = false;
> 
> 	sugov_iowait_boost(sg_cpu, time, flags);
> 	sg_cpu->last_update = time;
> @@ -457,7 +457,9 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
> 	if (!sugov_should_update_freq(sg_policy, time))
>		return;
> 
> -	busy = sugov_cpu_is_busy(sg_cpu);
> +	/* Limits may have changed, don't skip frequency update */
> +	if (!sg_policy->need_freq_update)
> +		busy = sugov_cpu_is_busy(sg_cpu);
> 
> 	util = sugov_get_util(sg_cpu);
>  	max = sg_cpu->max;
> -- 
> 2.21.0.rc0.269.g1a574e7a288b