linux-kernel - Re: [PATCH 00/14] sched/topology fixes

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Date:   Tue, 2 May 2017 11:54:47 -0300
From:   Lauro Venancio <lvenanci@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org
Cc:     lwang@...hat.com, riel@...hat.com, efault@....de,
        tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/14] sched/topology fixes

On 05/02/2017 11:43 AM, Peter Zijlstra wrote:
> On Fri, Apr 28, 2017 at 03:53:39PM +0200, Peter Zijlstra wrote:
>> Also, the following occurred to me:
>>
>>   sg_span & sg_mask == sg_mask
>>
>> Therefore, we don't need to do the whole "sg_span &" business.
>>
>> Hmm?
>> @@ -856,7 +857,7 @@ build_sched_groups(struct sched_domain *
>>  			continue;
>>  
>>  		group = get_group(i, sdd, &sg);
>> -		cpumask_setall(sched_group_mask(sg));
>> +		cpumask_copy(sched_group_mask(sg), sched_group_cpus(sg));
>>  
>>  		for_each_cpu(j, span) {
>>  			if (get_group(j, sdd, NULL) != group)
> OK, so this explodes mightily.
>
> That code also hurt my brain bad, so I had to fix that a little.
>
> The below seems to boot.
>
> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7996,7 +7996,7 @@ static int active_load_balance_cpu_stop(
>  static int should_we_balance(struct lb_env *env)
>  {
>  	struct sched_group *sg = env->sd->groups;
> -	struct cpumask *sg_cpus, *sg_mask;
> +	struct cpumask *sg_mask;
>  	int cpu, balance_cpu = -1;
>  
>  	/*
> @@ -8006,11 +8006,10 @@ static int should_we_balance(struct lb_e
>  	if (env->idle == CPU_NEWLY_IDLE)
>  		return 1;
>  
> -	sg_cpus = sched_group_cpus(sg);
>  	sg_mask = sched_group_mask(sg);
>  	/* Try to find first idle cpu */
> -	for_each_cpu_and(cpu, sg_cpus, env->cpus) {
> -		if (!cpumask_test_cpu(cpu, sg_mask) || !idle_cpu(cpu))
> +	for_each_cpu_and(cpu, sg_mask, env->cpus) {
> +		if (!idle_cpu(cpu))
>  			continue;
>  
>  		balance_cpu = cpu;
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -85,7 +85,8 @@ static int sched_domain_debug_one(struct
>  				group->sgc->id,
>  				cpumask_pr_args(sched_group_cpus(group)));
>  
> -		if ((sd->flags & SD_OVERLAP) && !cpumask_full(sched_group_mask(group))) {
> +		if ((sd->flags & SD_OVERLAP) &&
> +		    !cpumask_equal(sched_group_mask(group), sched_group_cpus(group))) {
>  			printk(KERN_CONT " mask=%*pbl",
>  				cpumask_pr_args(sched_group_mask(group)));
>  		}
> @@ -505,7 +506,7 @@ enum s_alloc {
>   */
>  int group_balance_cpu(struct sched_group *sg)
>  {
> -	return cpumask_first_and(sched_group_cpus(sg), sched_group_mask(sg));
> +	return cpumask_first(sched_group_mask(sg));
>  }
>  
>  
> @@ -833,23 +834,34 @@ build_overlap_sched_groups(struct sched_
>   * [*] in other words, the first group of each domain is its child domain.
>   */
>  
> -static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
> +static struct sched_group *get_group(int cpu, struct sd_data *sdd)
>  {
>  	struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
>  	struct sched_domain *child = sd->child;
> +	struct sched_group *sg;
>  
>  	if (child)
>  		cpu = cpumask_first(sched_domain_span(child));
>  
> -	if (sg) {
> -		*sg = *per_cpu_ptr(sdd->sg, cpu);
> -		(*sg)->sgc = *per_cpu_ptr(sdd->sgc, cpu);
> +	sg = *per_cpu_ptr(sdd->sg, cpu);
> +	sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);
>  
> -		/* For claim_allocations: */
> -		atomic_set(&(*sg)->sgc->ref, 1);
> +	/* For claim_allocations: */
> +	atomic_inc(&sg->ref);
> +	atomic_inc(&sg->sgc->ref);
> +
> +	if (child) {
> +		cpumask_copy(sched_group_cpus(sg), sched_domain_span(child));
> +		cpumask_copy(sched_group_mask(sg), sched_group_cpus(sg));
> +	} else {
> +		cpumask_set_cpu(cpu, sched_group_cpus(sg));
> +		cpumask_set_cpu(cpu, sched_group_cpus(sg));
Typo here. The mask is not being set in the else clause.

>  	}
>  
> -	return cpu;
> +	sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sched_group_cpus(sg));
> +	sg->sgc->min_capacity = SCHED_CAPACITY_SCALE;
> +
> +	return sg;
>  }
>  
>  /*
> @@ -868,34 +880,20 @@ build_sched_groups(struct sched_domain *
>  	struct cpumask *covered;
>  	int i;
>  
> -	get_group(cpu, sdd, &sd->groups);
> -	atomic_inc(&sd->groups->ref);
> -
> -	if (cpu != cpumask_first(span))
> -		return 0;
> -
>  	lockdep_assert_held(&sched_domains_mutex);
>  	covered = sched_domains_tmpmask;
>  
>  	cpumask_clear(covered);
>  
> -	for_each_cpu(i, span) {
> +	for_each_cpu_wrap(i, span, cpu) {
>  		struct sched_group *sg;
> -		int group, j;
>  
>  		if (cpumask_test_cpu(i, covered))
>  			continue;
>  
> -		group = get_group(i, sdd, &sg);
> -		cpumask_setall(sched_group_mask(sg));
> +		sg = get_group(i, sdd);
>  
> -		for_each_cpu(j, span) {
> -			if (get_group(j, sdd, NULL) != group)
> -				continue;
> -
> -			cpumask_set_cpu(j, covered);
> -			cpumask_set_cpu(j, sched_group_cpus(sg));
> -		}
> +		cpumask_or(covered, covered, sched_group_cpus(sg));
>  
>  		if (!first)
>  			first = sg;
> @@ -904,6 +902,7 @@ build_sched_groups(struct sched_domain *
>  		last = sg;
>  	}
>  	last->next = first;
> +	sd->groups = first;
>  
>  	return 0;
>  }