[S390] lockless idle time accounting
Martin Schwidefsky [Mon, 22 Jun 2009 10:08:20 +0000 (12:08 +0200)]
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>

arch/s390/include/asm/cputime.h
arch/s390/kernel/smp.c
arch/s390/kernel/vtime.c

index ec917d4..7a3817a 100644 (file)
@@ -178,7 +178,7 @@ cputime64_to_clock_t(cputime64_t cputime)
 }
 
 struct s390_idle_data {
-       spinlock_t lock;
+       unsigned int sequence;
        unsigned long long idle_count;
        unsigned long long idle_enter;
        unsigned long long idle_time;
index fd8e311..2270730 100644 (file)
@@ -856,13 +856,20 @@ static ssize_t show_idle_count(struct sys_device *dev,
 {
        struct s390_idle_data *idle;
        unsigned long long idle_count;
+       unsigned int sequence;
 
        idle = &per_cpu(s390_idle, dev->id);
-       spin_lock(&idle->lock);
+repeat:
+       sequence = idle->sequence;
+       smp_rmb();
+       if (sequence & 1)
+               goto repeat;
        idle_count = idle->idle_count;
        if (idle->idle_enter)
                idle_count++;
-       spin_unlock(&idle->lock);
+       smp_rmb();
+       if (idle->sequence != sequence)
+               goto repeat;
        return sprintf(buf, "%llu\n", idle_count);
 }
 static SYSDEV_ATTR(idle_count, 0444, show_idle_count, NULL);
@@ -872,15 +879,22 @@ static ssize_t show_idle_time(struct sys_device *dev,
 {
        struct s390_idle_data *idle;
        unsigned long long now, idle_time, idle_enter;
+       unsigned int sequence;
 
        idle = &per_cpu(s390_idle, dev->id);
-       spin_lock(&idle->lock);
        now = get_clock();
+repeat:
+       sequence = idle->sequence;
+       smp_rmb();
+       if (sequence & 1)
+               goto repeat;
        idle_time = idle->idle_time;
        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 sprintf(buf, "%llu\n", idle_time >> 12);
 }
 static SYSDEV_ATTR(idle_time_us, 0444, show_idle_time, NULL);
@@ -908,11 +922,7 @@ static int __cpuinit smp_cpu_notify(struct notifier_block *self,
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                idle = &per_cpu(s390_idle, cpu);
-               spin_lock_irq(&idle->lock);
-               idle->idle_enter = 0;
-               idle->idle_time = 0;
-               idle->idle_count = 0;
-               spin_unlock_irq(&idle->lock);
+               memset(idle, 0, sizeof(struct s390_idle_data));
                if (sysfs_create_group(&s->kobj, &cpu_online_attr_group))
                        return NOTIFY_BAD;
                break;
index ade17e7..c41bb0d 100644 (file)
@@ -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;
 }