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Date: Mon, 27 Jun 2016 18:21:11 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Mel Gorman <mgorman@techsingularity.net>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: [PATCH 4/5] sched/debug: remove several CONFIG_SCHEDSTATS guards
Message-ID: <20160627162111.GF30909@twins.programming.kicks-ass.net>
References: <cover.1466184592.git.jpoimboe@redhat.com>
 <e51e0ebe5af95ac295de720dd252e7c0d2142e4a.1466184592.git.jpoimboe@redhat.com>
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On Fri, Jun 17, 2016 at 12:43:26PM -0500, Josh Poimboeuf wrote:
> index 017a4f5..0aee5dd 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1626,10 +1626,15 @@ static inline int __set_cpus_allowed_ptr(struct task_struct *p,
>  static void
>  ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
>  {
> -#ifdef CONFIG_SCHEDSTATS
> -	struct rq *rq = this_rq();
> +	struct rq *rq;
> +
> +	if (!schedstat_enabled())
> +		return;
> +
> +	rq = this_rq();
>  
>  #ifdef CONFIG_SMP
> +{
>  	int this_cpu = smp_processor_id();
>  
>  	if (cpu == this_cpu) {
> @@ -1651,7 +1656,7 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
>  
>  	if (wake_flags & WF_MIGRATED)
>  		schedstat_inc(p->se.statistics.nr_wakeups_migrate);
> -
> +}
>  #endif /* CONFIG_SMP */
>  
>  	schedstat_inc(rq->ttwu_count);

I did:

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1636,10 +1636,7 @@ ttwu_stat(struct task_struct *p, int cpu
 	rq = this_rq();
 
 #ifdef CONFIG_SMP
-{
-	int this_cpu = smp_processor_id();
-
-	if (cpu == this_cpu) {
+	if (cpu == rq->cpu) {
 		schedstat_inc(rq->ttwu_local);
 		schedstat_inc(p->se.statistics.nr_wakeups_local);
 	} else {
@@ -1647,7 +1644,7 @@ ttwu_stat(struct task_struct *p, int cpu
 
 		schedstat_inc(p->se.statistics.nr_wakeups_remote);
 		rcu_read_lock();
-		for_each_domain(this_cpu, sd) {
+		for_each_domain(rq->cpu, sd) {
 			if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
 				schedstat_inc(sd->ttwu_wake_remote);
 				break;
@@ -1658,7 +1655,6 @@ ttwu_stat(struct task_struct *p, int cpu
 
 	if (wake_flags & WF_MIGRATED)
 		schedstat_inc(p->se.statistics.nr_wakeups_migrate);
-}
 #endif /* CONFIG_SMP */
 
 	schedstat_inc(rq->ttwu_count);