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Commit e98bbaaf authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

[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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 4f0076f7

arch/s390/include/asm/cputime.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

arch/s390/kernel/smp.c

+19 −9
Original line number Diff line number Diff line
@@ -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;

arch/s390/kernel/vtime.c

+15 −7
Original line number Diff line number Diff line
@@ -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;

}