linux-kernel - Re: [PATCH v5 04/12] sched: Allow all archs to set the capacity

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Message-ID: <20140910135039.GP3190@worktop.ger.corp.intel.com>
Date:	Wed, 10 Sep 2014 15:50:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, riel@...hat.com,
	Morten.Rasmussen@....com, efault@....de, nicolas.pitre@...aro.org,
	linaro-kernel@...ts.linaro.org, daniel.lezcano@...aro.org,
	dietmar.eggemann@....com
Subject: Re: [PATCH v5 04/12] sched: Allow all archs to set the capacity_orig

On Sat, Aug 30, 2014 at 10:37:40PM +0530, Preeti U Murthy wrote:
> > -	if ((sd->flags & SD_SHARE_CPUCAPACITY) && weight > 1) {
> > -		if (sched_feat(ARCH_CAPACITY))
> 
> Aren't you missing this check above? I understand that it is not
> crucial, but that would also mean removing ARCH_CAPACITY sched_feat
> altogether, wouldn't it?

Yes he's missing that, I added the below bit on top.

So the argument last time:
lkml.kernel.org/r/20140709105721.GT19379@...ns.programming.kicks-ass.net
was that you cannot put sched_feat(ARCH_CAPACITY) inside a weak arch_*
function. The test has to be outside, seeing how it needs to decide to
call the arch function at all (or revert to the default implementation).

---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5700,7 +5700,7 @@ unsigned long __weak arch_scale_freq_cap
 	return default_scale_capacity(sd, cpu);
 }
 
-unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
+static unsigned long default_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
 	if ((sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
 		return sd->smt_gain / sd->span_weight;
@@ -5708,6 +5708,11 @@ unsigned long __weak arch_scale_cpu_capa
 	return SCHED_CAPACITY_SCALE;
 }
 
+unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
+{
+	return default_scale_cpu_capacity(sd, cpu);
+}
+
 static unsigned long scale_rt_capacity(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
@@ -5747,7 +5752,10 @@ static void update_cpu_capacity(struct s
 	unsigned long capacity = SCHED_CAPACITY_SCALE;
 	struct sched_group *sdg = sd->groups;
 
-	capacity *= arch_scale_cpu_capacity(sd, cpu);
+	if (sched_feat(ARCH_CAPACITY))
+		capacity *= arch_scale_cpu_capacity(sd, cpu);
+	else
+		capacity *= default_scale_cpu_capacity(sd, cpu);
 
 	capacity >>= SCHED_CAPACITY_SHIFT;
 
--
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