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

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Date:   Fri, 28 Apr 2017 20:30:05 -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 04/28/2017 10:53 AM, Peter Zijlstra wrote:
> On Fri, Apr 28, 2017 at 03:19:58PM +0200, Peter Zijlstra wrote:
>> Hi,
>>
>> These patches are based upon the hard work of Lauro. He put in the time and
>> effort to understand and debug the code.
>>
>> So while I didn't take many of his actual patches; I want to thank him for
>> doing the work. Hopefully the "Debugged-by:" tag conveys some of that.
>>
>> In any case, please have a look. I think these should about cover things.
>>
>> Rik, Lauro, could you guys in particular look at the final patch that adds a
>> few comments. I attempted to document the intent and understanding there. But
>> given I've been staring at this stuff too long I could've missed the obvious.
>>
>> Comments and or suggestions welcome.
>>
> 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?
Agreed. Maybe we have to rename "mask" to something else. Maybe
"group_reached_by_cpus" or "group_installed_on_cpus".

>
> ---
> --- 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));
>  }
>  
>  
> @@ -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)