linux-kernel - Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection

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Message-ID: <20210525102945.GA24210@e120325.cambridge.arm.com>
Date:   Tue, 25 May 2021 11:29:46 +0100
From:   Beata Michalska <beata.michalska@....com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        corbet@....net, rdunlap@...radead.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry
 detection

On Tue, May 25, 2021 at 10:53:07AM +0100, Valentin Schneider wrote:
> On 24/05/21 23:55, Beata Michalska wrote:
> > On Mon, May 24, 2021 at 07:01:04PM +0100, Valentin Schneider wrote:
> >> On 24/05/21 11:16, Beata Michalska wrote:
> >> > This patch also removes the additional -dflags- parameter used when
> >>   ^^^^^^^^^^^^^^^^^^^^^^^
> >> s/^/Also remove/
> > I would kind of ... disagree.
> > All the commit msg is constructed using passive structure, the suggestion
> > would actually break that. And it does 'sound' bit imperative but I guess
> > that is subjective. I'd rather stay with impersonal structure (which is
> > applied through out the whole patchset).
> 
> It's mainly about the 'This patch' formulation, some take exception to that :-)
>
Will rephrase
> >>
> >> > building sched domains as the asymmetry flags are now being set
> >> > directly in sd_init.
> >> >
> >>
> >> Few nits below, but beyond that:
> >>
> >> Tested-by: Valentin Schneider <valentin.schneider@....com>
> >> Reviewed-by: Valentin Schneider <valentin.schneider@....com>
> >>
> > Thanks a lot for the review and testing!
> >
> >> > +static inline int
> >> > +asym_cpu_capacity_classify(struct sched_domain *sd,
> >> > +			   const struct cpumask *cpu_map)
> >> > +{
> >> > +	int sd_asym_flags = SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL;
> >> > +	struct asym_cap_data *entry;
> >> > +	int asym_cap_count = 0;
> >> > +
> >> > +	if (list_is_singular(&asym_cap_list))
> >> > +		goto leave;
> >> > +
> >> > +	list_for_each_entry(entry, &asym_cap_list, link) {
> >> > +		if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) {
> >> > +			++asym_cap_count;
> >> > +		} else {
> >> > +			/*
> >> > +			 * CPUs with given capacity might be offline
> >> > +			 * so make sure this is not the case
> >> > +			 */
> >> > +			if (cpumask_intersects(entry->cpu_mask, cpu_map)) {
> >> > +				sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL;
> >> > +				if (asym_cap_count > 1)
> >> > +					break;
> >> > +			}
> >>
> >> Readability nit: That could be made into an else if ().
> > It could but then this way the -comment- gets more exposed.
> > But that might be my personal perception so I can change that.
> 
> As always those are quite subjective! Methink something like this would
> still draw attention to the offline case:
> 
>                /*
>                 * Count how many unique capacities this domain covers. If a
>                 * capacity isn't covered, we need to check if any CPU with
>                 * that capacity is actually online, otherwise it can be
>                 * ignored.
>                 */
>                 if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) {
>                         ++asym_cap_count;
>                 } else if (cpumask_intersects(entry->cpu_mask, cpu_map)) {
>                         sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL;
>                         if (asym_cap_count > 1)
>                                 break;
>                 }
Noted.
Will wait for some more comments before sending out 'polished' version.

---
BR
B.