[S390] lockless idle time accounting

Replace the spinlock used in the idle time accounting with a sequence
counter mechanism analog to seqlock.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 15 insertions, 7 deletions

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index ade17e771f05..c41bb0d416e1 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -27,9 +27,7 @@
 
 static DEFINE_PER_CPU(struct vtimer_queue, virt_cpu_timer);
 
-DEFINE_PER_CPU(struct s390_idle_data, s390_idle) = {
-	.lock = __SPIN_LOCK_UNLOCKED(s390_idle.lock)
-};
+DEFINE_PER_CPU(struct s390_idle_data, s390_idle);
 
 static inline __u64 get_vtimer(void)
 {
@@ -151,11 +149,13 @@ void vtime_start_cpu(void)
 		vq->elapsed -= vq->idle - S390_lowcore.async_enter_timer;
 	}
 
-	spin_lock(&idle->lock);
+	idle->sequence++;
+	smp_wmb();
 	idle->idle_time += idle_time;
 	idle->idle_enter = 0ULL;
 	idle->idle_count++;
-	spin_unlock(&idle->lock);
+	smp_wmb();
+	idle->sequence++;
 }
 
 void vtime_stop_cpu(void)
@@ -242,15 +242,23 @@ cputime64_t s390_get_idle_time(int cpu)
 {
 	struct s390_idle_data *idle;
 	unsigned long long now, idle_time, idle_enter;
+	unsigned int sequence;
 
 	idle = &per_cpu(s390_idle, cpu);
-	spin_lock(&idle->lock);
+
 	now = get_clock();
+repeat:
+	sequence = idle->sequence;
+	smp_rmb();
+	if (sequence & 1)
+		goto repeat;
 	idle_time = 0;
 	idle_enter = idle->idle_enter;
 	if (idle_enter != 0ULL && idle_enter < now)
 		idle_time = now - idle_enter;
-	spin_unlock(&idle->lock);
+	smp_rmb();
+	if (idle->sequence != sequence)
+		goto repeat;
 	return idle_time;
 }