Re: [PATCH] sched/fair: Remove idle_balance() declaration in sched.h

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Feb 11, 2014 at 04:01:04PM +0100, Daniel Lezcano wrote:
> The idle_balance() function is called within a #ifdef CONFIG_SMP section.
> 
> Remove its declaration in sched.h for !CONFIG_SMP because it is pointless.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

The below again makes a horrible mess of idle_balance() -- which you
tried to clean up.. but it does rid us of some #ifdef goo.

Hmmm?

---
 kernel/sched/fair.c  | 47 +++++++++++++++++++++++++++++------------------
 kernel/sched/sched.h |  7 -------
 2 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 235cfa7ad8fc..d168c968195b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2374,13 +2374,13 @@ static inline void __update_group_entity_contrib(struct sched_entity *se)
 		se->avg.load_avg_contrib >>= NICE_0_SHIFT;
 	}
 }
-#else
+#else /* CONFIG_FAIR_GROUP_SCHED */
 static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
 						 int force_update) {}
 static inline void __update_tg_runnable_avg(struct sched_avg *sa,
 						  struct cfs_rq *cfs_rq) {}
 static inline void __update_group_entity_contrib(struct sched_entity *se) {}
-#endif
+#endif /* CONFIG_FAIR_GROUP_SCHED */
 
 static inline void __update_task_entity_contrib(struct sched_entity *se)
 {
@@ -2571,6 +2571,8 @@ void idle_exit_fair(struct rq *this_rq)
 	update_rq_runnable_avg(this_rq, 0);
 }
 
+static int idle_balance(struct rq *this_rq);
+
 #else /* CONFIG_SMP */
 
 static inline void update_entity_load_avg(struct sched_entity *se,
@@ -2584,6 +2586,12 @@ static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,
 					   int sleep) {}
 static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
 					      int force_update) {}
+
+static inline int idle_balance(struct rq *rq)
+{
+	return 0;
+}
+
 #endif /* CONFIG_SMP */
 
 static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -4677,7 +4685,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev)
 	struct sched_entity *se;
 	struct task_struct *p;
 
-again: __maybe_unused
+again:
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	if (!cfs_rq->nr_running)
 		goto idle;
@@ -4775,18 +4783,8 @@ again: __maybe_unused
 	return p;
 
 idle:
-#ifdef CONFIG_SMP
-	idle_enter_fair(rq);
-	/*
-	 * We must set idle_stamp _before_ calling idle_balance(), such that we
-	 * measure the duration of idle_balance() as idle time.
-	 */
-	rq->idle_stamp = rq_clock(rq);
-	if (idle_balance(rq)) { /* drops rq->lock */
-		rq->idle_stamp = 0;
+	if (idle_balance(rq)) /* drops rq->lock */
 		goto again;
-	}
-#endif
 
 	return NULL;
 }
@@ -6634,7 +6632,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
  * idle_balance is called by schedule() if this_cpu is about to become
  * idle. Attempts to pull tasks from other CPUs.
  */
-int idle_balance(struct rq *this_rq)
+static int idle_balance(struct rq *this_rq)
 {
 	struct sched_domain *sd;
 	int pulled_task = 0;
@@ -6642,8 +6640,15 @@ int idle_balance(struct rq *this_rq)
 	u64 curr_cost = 0;
 	int this_cpu = this_rq->cpu;
 
+	idle_enter_fair(this_rq);
+	/*
+	 * We must set idle_stamp _before_ calling idle_balance(), such that we
+	 * measure the duration of idle_balance() as idle time.
+	 */
+	this_rq->idle_stamp = rq_clock(this_rq);
+
 	if (this_rq->avg_idle < sysctl_sched_migration_cost)
-		return 0;
+		goto out;
 
 	/*
 	 * Drop the rq->lock, but keep IRQ/preempt disabled.
@@ -6692,8 +6697,10 @@ int idle_balance(struct rq *this_rq)
 	 * While browsing the domains, we released the rq lock.
 	 * A task could have be enqueued in the meantime
 	 */
-	if (this_rq->nr_running && !pulled_task)
-		return 1;
+	if (this_rq->nr_running && !pulled_task) {
+		pulled_task = 1;
+		goto out;
+	}
 
 	if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
 		/*
@@ -6706,6 +6713,10 @@ int idle_balance(struct rq *this_rq)
 	if (curr_cost > this_rq->max_idle_balance_cost)
 		this_rq->max_idle_balance_cost = curr_cost;
 
+out:
+	if (pulled_task)
+		this_rq->idle_stamp = 0;
+
 	return pulled_task;
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1bf34c257d3b..92018f9821e8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1163,17 +1163,10 @@ extern const struct sched_class idle_sched_class;
 extern void update_group_power(struct sched_domain *sd, int cpu);
 
 extern void trigger_load_balance(struct rq *rq);
-extern int idle_balance(struct rq *this_rq);
 
 extern void idle_enter_fair(struct rq *this_rq);
 extern void idle_exit_fair(struct rq *this_rq);
 
-#else	/* CONFIG_SMP */
-
-static inline void idle_balance(int cpu, struct rq *rq)
-{
-}
-
 #endif
 
 extern void sysrq_sched_debug_show(void);