linux-kernel - Re: [PATCH v2 7/8] sched/schedutil: Add a new tunable to dictate response time

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Date: Thu, 1 Feb 2024 22:31:29 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Lukasz Luba <lukasz.luba@....com>, Wei Wang <wvw@...gle.com>,
	Rick Yiu <rickyiu@...gle.com>, Chung-Kai Mei <chungkai@...gle.com>
Subject: Re: [PATCH v2 7/8] sched/schedutil: Add a new tunable to dictate
 response time

On 12/08/23 00:23, Qais Yousef wrote:

> +static inline u64 sugov_calc_freq_response_ms(struct sugov_policy *sg_policy)
> +{
> +	int cpu = cpumask_first(sg_policy->policy->cpus);
> +	unsigned long cap = arch_scale_cpu_capacity(cpu);
> +	unsigned int max_freq, sec_max_freq;
> +
> +	max_freq = sg_policy->policy->cpuinfo.max_freq;
> +	sec_max_freq = __resolve_freq(sg_policy->policy,
> +				      max_freq - 1,
> +				      CPUFREQ_RELATION_H);
> +
> +	/*
> +	 * We will request max_freq as soon as util crosses the capacity at
> +	 * second highest frequency. So effectively our response time is the
> +	 * util at which we cross the cap@..._highest_freq.
> +	 */
> +	cap = sec_max_freq * cap / max_freq;
> +
> +	return approximate_runtime(cap + 1);

After Linus problem (and more testing) I realize this is not correct. This
value is correct for the biggest core only, for smaller cores I must stretch
time with capacity. I have similar invariance issues that I need to address in
this series and uclamp max aggregation series.