[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>
diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index ec917d4..7a3817a 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -178,7 +178,7 @@
}
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;
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index fd8e311..2270730 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -856,13 +856,20 @@
{
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 @@
{
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 @@
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;
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index ade17e7..c41bb0d 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 @@
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 @@
{
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;
}