Subject: Re: [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU

From: Mel Gorman <[email-masked]>
Date: Tue, 8 Dec 2020 13:36:50 +0000

On Tue, Dec 08, 2020 at 02:24:32PM +0100, Vincent Guittot wrote:
> > > Nitpick:
> > >
> > > Since now avg_cost and avg_idle are only used w/ SIS_PROP, they could go
> > > completely into the SIS_PROP if condition.
> > >
> >
> > Yeah, I can do that. In the initial prototype, that happened in a
> > separate patch that split out SIS_PROP into a helper function and I
> > never merged it back. It's a trivial change.
> 
> while doing this, should you also put the update of
> this_sd->avg_scan_cost under the SIS_PROP feature ?
> 

It's outside the scope of the series but why not. This?

--8<--
sched/fair: Move avg_scan_cost calculations under SIS_PROP

As noted by Vincent Guittot, avg_scan_costs are calculated for SIS_PROP
even if SIS_PROP is disabled. Move the time calculations under a SIS_PROP
check and while we are at it, exclude the cost of initialising the CPU
mask from the average scan cost.

Signed-off-by: Mel Gorman <[email-masked]>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 19ca0265f8aa..0fee53b1aae4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6176,10 +6176,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 			nr = 4;
 	}
 
-	time = cpu_clock(this);
-
 	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
 
+	if (sched_feat(SIS_PROP))
+		time = cpu_clock(this);
 	for_each_cpu_wrap(cpu, cpus, target) {
 		if (!--nr)
 			return -1;
@@ -6187,8 +6187,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 			break;
 	}
 
-	time = cpu_clock(this) - time;
-	update_avg(&this_sd->avg_scan_cost, time);
+	if (sched_feat(SIS_PROP)) {
+		time = cpu_clock(this) - time;
+		update_avg(&this_sd->avg_scan_cost, time);
+	}
 
 	return cpu;
 }

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