linux-kernel - Re: [PATCH v3 2/2] cpufreq: schedutil: Cleanup and document iowait boost

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Date:   Mon, 21 May 2018 16:02:56 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 2/2] cpufreq: schedutil: Cleanup and document iowait
 boost

On 21-05-18, 11:11, Patrick Bellasi wrote:
> On 21-May 15:22, Viresh Kumar wrote:
> > On 21-05-18, 09:51, Patrick Bellasi wrote:
> > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > > +static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> > > +			       unsigned int flags)
> > > +{
> > > +	bool set_iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
> > > +
> > > +	/* Reset boost if the CPU appears to have been idle enough */
> > > +	if (sg_cpu->iowait_boost &&
> > > +	    sugov_iowait_reset(sg_cpu, time, set_iowait_boost))
> > > +		return;
> > > +
> > > +	/* Boost only tasks waking up after IO */
> > > +	if (!set_iowait_boost)
> > > +		return;
> > > +
> > > +	/* Ensure boost doubles only one time at each request */
> > > +	if (sg_cpu->iowait_boost_pending)
> > > +		return;
> > > +	sg_cpu->iowait_boost_pending = true;
> > > +
> > > +	/* Double the boost at each request */
> > > +	if (sg_cpu->iowait_boost) {
> > > +		sg_cpu->iowait_boost <<= 1;
> > > +		if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
> > > +			sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
> > > +		return;
> > 
> > Maybe add "else" part of the if block and drop the "return" statement
> > here ?
> 
> If not "mandatory", I would prefer as it is: I'm running with a small
> stack size in my mind. :)
> 
> This "bail out of a function as soon as possible" template allows me
> to see immediately that, for example in this function, once we decided
> to double the boost value there is anything more to do here.
> 
> At the same time, the statement below it reads as the function
> default action.
> 
> Does it make any sense?
> 
> [...]
> 
> > > +	/*
> > > +	 * Apply the current boost value: a CPU is boosted only if its current
> > > +	 * utilization is smaller then the current IO boost level.
> > > +	 */
> > >  	boost_util = sg_cpu->iowait_boost;
> > >  	boost_max = sg_cpu->iowait_boost_max;
> > > -
> > 
> > Maybe keep this blank line as is ?
> 
> I've removed it because the above comment now refers to all these
> lines together.

Okay for both.

-- 
viresh