linux-kernel - Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

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Date:   Fri, 22 Dec 2017 11:02:06 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

On 22-Dec 11:06, Peter Zijlstra wrote:
> On Wed, Dec 20, 2017 at 06:38:14PM +0100, Juri Lelli wrote:
> > On 20/12/17 16:30, Peter Zijlstra wrote:
> > 
> > [...]
> > 
> > > @@ -327,12 +331,7 @@ static unsigned int sugov_next_freq_shar
> > >  		if (delta_ns > TICK_NSEC) {
> > >  			j_sg_cpu->iowait_boost = 0;
> > >  			j_sg_cpu->iowait_boost_pending = false;
> > > -			j_sg_cpu->util_cfs = 0;
> > > -			if (j_sg_cpu->util_dl == 0)
> > > -				continue;
> > >  		}
> > 
> > This goes away because with Brendan/Vincent fix we don't need the
> > workaround for stale CFS util contribution for idle CPUs anymore?
> 
> An easy fix would be something like the below I suppose (also folded a
> change from Viresh).
> 
> This way it completely ignores the demand from idle CPUs. Which I
> suppose is exactly what you want, no?
> 
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index ab84d2261554..9736b537386a 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -315,8 +315,8 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>  		unsigned long j_util, j_max;
>  		s64 delta_ns;
>  
> -		if (j_sg_cpu != sg_cpu)
> -			sugov_get_util(j_sg_cpu);
> +		if (idle_cpu(j))
> +			continue;

That should work to skip IDLE CPUs... however I'm missing where now we
get the sugov_get_util(j_sg_cpu) for active CPUs. It has been moved
somewhere else I guess...

Moreover, that way don't we completely disregard CFS blocked load for
IDLE CPUs... as well as DL reserved utilization, which should be
released only at the 0-lag time?

>  
>  		/*
>  		 * If the CFS CPU utilization was last updated before the
> @@ -354,7 +354,6 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  
>  	raw_spin_lock(&sg_policy->update_lock);
>  
> -	sugov_get_util(sg_cpu);
>  	sugov_set_iowait_boost(sg_cpu, time, flags);
>  	sg_cpu->last_update = time;
>  

-- 
#include <best/regards.h>

Patrick Bellasi