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

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Message-ID: <20210526214308.GB1712@e120325.cambridge.arm.com>
Date:   Wed, 26 May 2021 22:43:08 +0100
From:   Beata Michalska <beata.michalska@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, corbet@....net, rdunlap@...radead.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry
 detection

On Wed, May 26, 2021 at 08:17:25PM +0200, Dietmar Eggemann wrote:
> On 26/05/2021 14:15, Beata Michalska wrote:
> > On Wed, May 26, 2021 at 11:52:25AM +0200, Dietmar Eggemann wrote:
> >> On 25/05/2021 12:29, Beata Michalska wrote:
> >>> 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:
> 
> [...]
> 
> >> static inline int
> >> asym_cpu_capacity_classify(struct sched_domain *sd, 
> >>                            const struct cpumask *cpu_map)
> >> {
> >>         int sd_span_match = 0, cpu_map_match = 0, flags = 0; 
> >>         struct asym_cap_data *entry;
> >>
> >>         list_for_each_entry(entry, &asym_cap_list, link) {
> >>                 if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask))
> >>                         ++sd_span_match;
> >>                 else if (cpumask_intersects(cpu_map, entry->cpu_mask))
> >>                         ++cpu_map_match;
> >>         }
> >>
> >>         WARN_ON_ONCE(!sd_span_match);
> >>
> >>         if (sd_span_match > 1) { 
> >>                 flags |= SD_ASYM_CPUCAPACITY;
> >>                 if (!cpu_map_match)
> >>                         flags |= SD_ASYM_CPUCAPACITY_FULL;
> >>         }
> >>
> >>         return flags;
> >> }
> > So I planned to drop the list_is_singular check as it is needless really.
> > Otherwise, I am not really convinced by the suggestion. I could add comments
> > around current version to make it more ..... 'digestible' but I'd rather
> > stay with it as it seems more compact to me (subjective).
> 
> You could pass in `const struct cpumask *sd_span` instead of `struct
> sched_domain *sd` though. To make it clear that both masks are used to
> compare against the cpumasks of the asym_cap_list entries.
>
I could definitely do that, though if I switch to arrays for CPUs masks,
it might get a bit confusing again.
No strong preferences here though. Can do either or both.

Thanks.

---
BR
B.
>  static inline int
> -asym_cpu_capacity_classify(struct sched_domain *sd,
> +asym_cpu_capacity_classify(const struct cpumask *sd_span,
>  			   const struct cpumask *cpu_map)
>  {
>  	int sd_asym_flags = SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL;
> @@ -1377,14 +1378,14 @@ asym_cpu_capacity_classify(struct sched_domain *sd,
>  		goto leave;
>  
>  	list_for_each_entry(entry, &asym_cap_list, link) {
> -		if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) {
> +		if (cpumask_intersects(sd_span, 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)) {
> +			if (cpumask_intersects(cpu_map, entry->cpu_mask)) {
>  				sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL;
>  				if (asym_cap_count > 1)
>  					break;
> @@ -1395,7 +1396,6 @@ asym_cpu_capacity_classify(struct sched_domain *sd,
>  leave:
>  	return asym_cap_count > 1 ? sd_asym_flags : 0;
>  }
> -#endif
>  
>  static inline struct asym_cap_data *
>  asym_cpu_capacity_get_data(unsigned long capacity)
> @@ -1589,6 +1589,7 @@ sd_init(struct sched_domain_topology_level *tl,
>  	struct sd_data *sdd = &tl->data;
>  	struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
>  	int sd_id, sd_weight, sd_flags = 0;
> +	struct cpumask *sd_span;
>  
>  #ifdef CONFIG_NUMA
>  	/*
> @@ -1636,10 +1637,11 @@ sd_init(struct sched_domain_topology_level *tl,
>  #endif
>  	};
>  
> -	cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu));
> -	sd_id = cpumask_first(sched_domain_span(sd));
> +	sd_span = sched_domain_span(sd);
> +	cpumask_and(sd_span, cpu_map, tl->mask(cpu));
> +	sd_id = cpumask_first(sd_span);
>  
> -	sd->flags |= asym_cpu_capacity_classify(sd, cpu_map);
> +	sd->flags |= asym_cpu_capacity_classify(sd_span, cpu_map);
>  	/*
>  	 * Convert topological properties into behaviour.
>  	 */