sched: kill sync_cpu maintenance

We assume boot CPU as a sync CPU and initialize it's window_start
to sched_ktime_clock(). As windows are synchronized across all
CPUs, the secondary CPUs' window_start are initialized from the
sync_cpu's window_start. A CPU's window_start is never reset, so
this synchronization happens only once for a given CPU. Given this
fact, there is no need to reassigning the sync_cpu role to another
CPU when the boot CPU is going offline. Remove this unnecessary
maintenance of sync_cpu and use any online CPU's window_start as
reference.

Change-Id: I169a8e80573c6dbcb1edeab0659c07c17102f4c9
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>

3 files changed, 6 insertions, 16 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 76cbd55e99ac..519aee32e122 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5905,7 +5905,6 @@ int sched_isolate_cpu(int cpu)
 	smp_call_function_any(&avail_cpus, hrtimer_quiesce_cpu, &cpu, 1);
 	smp_call_function_any(&avail_cpus, timer_quiesce_cpu, &cpu, 1);
 
-	migrate_sync_cpu(cpu, cpumask_first(&avail_cpus));
 	stop_cpus(cpumask_of(cpu), do_isolation_work_cpu_stop, 0);
 
 	calc_load_migrate(rq);
@@ -6286,7 +6285,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
 		sched_ttwu_pending();
 		/* Update our root-domain */
 		raw_spin_lock_irqsave(&rq->lock, flags);
-		migrate_sync_cpu(cpu, smp_processor_id());
 
 		if (rq->rd) {
 			BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
diff --git a/kernel/sched/hmp.c b/kernel/sched/hmp.c
index 443f16732414..433d19663496 100644
--- a/kernel/sched/hmp.c
+++ b/kernel/sched/hmp.c
@@ -788,8 +788,6 @@ __read_mostly unsigned int sched_ravg_window = MIN_SCHED_RAVG_WINDOW;
 /* Temporarily disable window-stats activity on all cpus */
 unsigned int __read_mostly sched_disable_window_stats;
 
-static unsigned int sync_cpu;
-
 struct related_thread_group *related_thread_groups[MAX_NUM_CGROUP_COLOC_ID];
 static LIST_HEAD(active_related_thread_groups);
 static DEFINE_RWLOCK(related_thread_group_lock);
@@ -3015,18 +3013,20 @@ void mark_task_starting(struct task_struct *p)
 
 void set_window_start(struct rq *rq)
 {
-	int cpu = cpu_of(rq);
-	struct rq *sync_rq = cpu_rq(sync_cpu);
+	static int sync_cpu_available;
 
 	if (rq->window_start || !sched_enable_hmp)
 		return;
 
-	if (cpu == sync_cpu) {
+	if (!sync_cpu_available) {
 		rq->window_start = sched_ktime_clock();
+		sync_cpu_available = 1;
 	} else {
+		struct rq *sync_rq = cpu_rq(cpumask_any(cpu_online_mask));
+
 		raw_spin_unlock(&rq->lock);
 		double_rq_lock(rq, sync_rq);
-		rq->window_start = cpu_rq(sync_cpu)->window_start;
+		rq->window_start = sync_rq->window_start;
 		rq->curr_runnable_sum = rq->prev_runnable_sum = 0;
 		rq->nt_curr_runnable_sum = rq->nt_prev_runnable_sum = 0;
 		raw_spin_unlock(&sync_rq->lock);
@@ -3035,12 +3035,6 @@ void set_window_start(struct rq *rq)
 	rq->curr->ravg.mark_start = rq->window_start;
 }
 
-void migrate_sync_cpu(int cpu, int new_cpu)
-{
-	if (cpu == sync_cpu)
-		sync_cpu = new_cpu;
-}
-
 static void reset_all_task_stats(void)
 {
 	struct task_struct *g, *p;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a9d98b7dd10e..d907eeb297a3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1123,7 +1123,6 @@ extern void clear_boost_kick(int cpu);
 extern void clear_hmp_request(int cpu);
 extern void mark_task_starting(struct task_struct *p);
 extern void set_window_start(struct rq *rq);
-extern void migrate_sync_cpu(int cpu, int new_cpu);
 extern void update_cluster_topology(void);
 extern void note_task_waking(struct task_struct *p, u64 wallclock);
 extern void set_task_last_switch_out(struct task_struct *p, u64 wallclock);
@@ -1525,7 +1524,6 @@ static inline void clear_boost_kick(int cpu) { }
 static inline void clear_hmp_request(int cpu) { }
 static inline void mark_task_starting(struct task_struct *p) { }
 static inline void set_window_start(struct rq *rq) { }
-static inline void migrate_sync_cpu(int cpu, int new_cpu) {}
 static inline void init_clusters(void) {}
 static inline void update_cluster_topology(void) { }
 static inline void note_task_waking(struct task_struct *p, u64 wallclock) { }