linux-kernel - Re: [PATCH v4 10/10] sched/fair: Provide idle search schedstats

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Date:   Fri, 7 Dec 2018 11:56:23 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Steve Sistare <steven.sistare@...cle.com>, mingo@...hat.com,
        peterz@...radead.org
Cc:     subhra.mazumdar@...cle.com, dhaval.giani@...cle.com,
        daniel.m.jordan@...cle.com, pavel.tatashin@...rosoft.com,
        matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
        riel@...hat.com, jbacik@...com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, quentin.perret@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/10] sched/fair: Provide idle search schedstats

Hi Steve,

On 06/12/2018 21:28, Steve Sistare wrote:
[...]
> @@ -6392,6 +6422,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
>  static int
>  select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
>  {
> +	unsigned long time = schedstat_start_time();

With arm64's defconfig (!CONFIG_SCHEDSTATS) I get:

kernel/sched/fair.c: In function ‘select_task_rq_fair’:
kernel/sched/fair.c:6459:16: warning: unused variable ‘time’ [-Wunused-variable]
  unsigned long time = schedstat_start_time();
                ^~~~

So you probably want something like this:

----->8-----
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5a113a8..7d33f74 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6456,12 +6456,14 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
 static int
 select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
 {
-	unsigned long time = schedstat_start_time();
 	struct sched_domain *tmp, *sd = NULL;
 	int cpu = smp_processor_id();
 	int new_cpu = prev_cpu;
 	int want_affine = 0;
 	int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING);
+	unsigned long time;
+
+	time = schedstat_start_time();
 
 	if (sd_flag & SD_BALANCE_WAKE) {
 		record_wakee(p);
-----8<-----

The 0-day bot will catch those but since it's the only warn I got I figured
I'd report it :)

>  	struct sched_domain *tmp, *sd = NULL;
>  	int cpu = smp_processor_id();
>  	int new_cpu = prev_cpu;
[...]