linux-kernel - Re: [PATCH RFC v5] cpufreq: schedutil: Make iowait boost more energy efficient

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Date:   Wed, 19 Jul 2017 11:07:11 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Juri Lelli <juri.lelli@....com>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Andres Oportus <andresoportus@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH RFC v5] cpufreq: schedutil: Make iowait boost more energy
 efficient

On 18-07-17, 15:02, Juri Lelli wrote:
> Mmm, seems to make sense to me. :/
> 
> Would the following work (on top of Joel's v5)? Rationale being that
> only in sugov_set_iowait_boost we might bump freq up (if no iowait_boost
> was set) or start from policy->min. In sugov_iowait_boost (consumer)
> instead we do the decay (if no boosting was pending).
> 
> ---
>  kernel/sched/cpufreq_schedutil.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 46b2479641cc..b270563c15a5 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -171,8 +171,14 @@ static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
>  {
>  	if (flags & SCHED_CPUFREQ_IOWAIT) {
>  		sg_cpu->iowait_boost_pending = true;
> -		sg_cpu->iowait_boost = max(sg_cpu->iowait_boost,
> -					   sg_cpu->sg_policy->policy->min);
> +		if (sg_cpu->iowait_boost) {
> +			/* Bump up 2*current_boost until hitting max */
> +			sg_cpu->iowait_boost = max(sg_cpu->iowait_boost << 1,
> +						   sg_cpu->iowait_boost_max);

And we are back at where we started :)

This wouldn't work because sugov_set_iowait_boost() gets called a lot.
Maybe 10 times within a rate_limit_us period.

The thumb rule is, never double/half the boost from
sugov_set_iowait_boost() :)

-- 
viresh