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

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Date:   Fri, 28 Apr 2017 15:53:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, lvenanci@...hat.com
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 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?

---
--- 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)