linux-kernel - [PATCH 2/2] sched: add for_each_sched

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Date: Fri, 16 Feb 2024 22:55:47 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	"Joel Fernandes (Google)" <joel@...lfernandes.org>,
	Len Brown <len.brown@...el.com>,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] sched: add for_each_sched_group() and use everywhere

Make code iterating over all sched_groups more straightforward.

Note: There's no point in WARN_ON in init_sched_groups_capacity() if
we're going to unconditionally dereference a NULL pointer just a few
instructions later.

Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
---
 kernel/sched/fair.c     | 13 +++++--------
 kernel/sched/sched.h    |  5 +++++
 kernel/sched/topology.c | 19 ++++++-------------
 3 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7ac9f4b1d955..a8a011f24a6d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9566,15 +9566,13 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
 		 * span the current group.
 		 */
 
-		group = child->groups;
-		do {
+		for_each_sched_group(child, group) {
 			struct sched_group_capacity *sgc = group->sgc;
 
 			capacity += sgc->capacity;
 			min_capacity = min(sgc->min_capacity, min_capacity);
 			max_capacity = max(sgc->max_capacity, max_capacity);
-			group = group->next;
-		} while (group != child->groups);
+		}
 	}
 
 	sdg->sgc->capacity = capacity;
@@ -10549,13 +10547,13 @@ static void update_idle_cpu_scan(struct lb_env *env,
 
 static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
 {
-	struct sched_group *sg = env->sd->groups;
 	struct sg_lb_stats *local = &sds->local_stat;
 	struct sg_lb_stats tmp_sgs;
 	unsigned long sum_util = 0;
+	struct sched_group *sg;
 	int sg_status = 0;
 
-	do {
+	for_each_sched_group(env->sd, sg) {
 		struct sg_lb_stats *sgs = &tmp_sgs;
 		int local_group;
 
@@ -10586,8 +10584,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
 		sds->total_capacity += sgs->group_capacity;
 
 		sum_util += sgs->group_util;
-		sg = sg->next;
-	} while (sg != env->sd->groups);
+	}
 
 	/*
 	 * Indicate that the child domain of the busiest group prefers tasks
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2e5a95486a42..88f3cba60b1e 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1902,6 +1902,11 @@ struct sched_group {
 	unsigned long		cpumask[];
 };
 
+#define for_each_sched_group(sd, sg) \
+	for ((sg) = NULL; \
+	     likely((sg)) ? (sg) != (sd)->groups : ((((sg) = (sd)->groups)), 1); \
+	     (void)((((sg) = (sg)->next)) || ({ BUG(); 0; })))
+
 static inline struct cpumask *sched_group_span(struct sched_group *sg)
 {
 	return to_cpumask(sg->cpumask);
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 75b1a18783c2..dce29cf28f32 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -758,17 +758,15 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 		sd = sd->parent;
 		destroy_sched_domain(tmp);
 		if (sd) {
-			struct sched_group *sg = sd->groups;
+			struct sched_group *sg;
 
 			/*
 			 * sched groups hold the flags of the child sched
 			 * domain for convenience. Clear such flags since
 			 * the child is being destroyed.
 			 */
-			do {
+			for_each_sched_group(sd, sg)
 				sg->flags = 0;
-				sg = sg->next;
-			} while (sg != sd->groups);
 
 			sd->child = NULL;
 		}
@@ -1290,12 +1288,10 @@ build_sched_groups(struct sched_domain *sd, int cpu)
  */
 static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
 {
-	struct sched_group *sg = sd->groups;
 	struct cpumask *mask = sched_domains_tmpmask2;
+	struct sched_group *sg;
 
-	WARN_ON(!sg);
-
-	do {
+	for_each_sched_group(sd, sg) {
 		int cpu, cores = 0, max_cpu = -1;
 
 		sg->group_weight = cpumask_weight(sched_group_span(sg));
@@ -1310,7 +1306,7 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
 		sg->cores = cores;
 
 		if (!(sd->flags & SD_ASYM_PACKING))
-			goto next;
+			continue;
 
 		for_each_cpu(cpu, sched_group_span(sg)) {
 			if (max_cpu < 0)
@@ -1319,10 +1315,7 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
 				max_cpu = cpu;
 		}
 		sg->asym_prefer_cpu = max_cpu;
-
-next:
-		sg = sg->next;
-	} while (sg != sd->groups);
+	}
 
 	if (cpu != group_balance_cpu(sg))
 		return;
-- 
2.39.2