linux-kernel - Re: [PATCH v9 09/15] sched: Introduce sched_energy

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Date:   Wed, 21 Nov 2018 14:08:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...eaurora.org,
        skannan@...eaurora.org, pkondeti@...eaurora.org,
        juri.lelli@...hat.com, edubezval@...il.com,
        srinivas.pandruvada@...ux.intel.com, currojerez@...eup.net,
        javi.merino@...nel.org
Subject: Re: [PATCH v9 09/15] sched: Introduce sched_energy_present static key

On Mon, Nov 19, 2018 at 02:18:51PM +0000, Quentin Perret wrote:

> +static void sched_energy_start(int ndoms_new, cpumask_var_t doms_new[])
> +{
> +	/*
> +	 * The conditions for EAS to start are checked during the creation of
> +	 * root domains. If one of them meets all conditions, it will have a
> +	 * non-null list of performance domains.
> +	 */
> +	while (ndoms_new) {
> +		if (cpu_rq(cpumask_first(doms_new[ndoms_new - 1]))->rd->pd)
> +			goto enable;
> +		ndoms_new--;
> +	}

That seems quite ugly; can't you simply return a bool from
build_perf_domains() ?

Something like the below, but less fugly ;-)

--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -299,7 +299,7 @@ static void destroy_perf_domain_rcu(stru
 #define EM_MAX_COMPLEXITY 2048
 
 extern struct cpufreq_governor schedutil_gov;
-static void build_perf_domains(const struct cpumask *cpu_map)
+static bool build_perf_domains(const struct cpumask *cpu_map)
 {
 	int i, nr_pd = 0, nr_cs = 0, nr_cpus = cpumask_weight(cpu_map);
 	struct perf_domain *pd = NULL, *tmp;
@@ -365,7 +365,7 @@ static void build_perf_domains(const str
 	if (tmp)
 		call_rcu(&tmp->rcu, destroy_perf_domain_rcu);
 
-	return;
+	return !!pd;
 
 free:
 	free_pd(pd);
@@ -373,6 +373,8 @@ static void build_perf_domains(const str
 	rcu_assign_pointer(rd->pd, NULL);
 	if (tmp)
 		call_rcu(&tmp->rcu, destroy_perf_domain_rcu);
+
+	return false;
 }
 #else
 static void free_pd(struct perf_domain *pd) { }
@@ -2173,6 +2175,9 @@ void partition_sched_domains(int ndoms_n
 	}
 
 #if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
+	{
+	bool has_eas = false;
+
 	/* Build perf. domains: */
 	for (i = 0; i < ndoms_new; i++) {
 		for (j = 0; j < n && !sched_energy_update; j++) {
@@ -2181,10 +2186,13 @@ void partition_sched_domains(int ndoms_n
 				goto match3;
 		}
 		/* No match - add perf. domains for a new rd */
-		build_perf_domains(doms_new[i]);
+		has_eas |= build_perf_domains(doms_new[i]);
 match3:
 		;
 	}
+
+	sched_energy_set(has_eas);
+	}
 #endif
 
 	/* Remember the new sched domains: */