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[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>
This commit is contained in:
Martin Schwidefsky 2009-06-22 12:08:20 +02:00
parent 4f0076f77f
commit e98bbaafcd
3 changed files with 35 additions and 17 deletions
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2
arch/s390/include/asm/cputime.h
View 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;

28
arch/s390/kernel/smp.c
View 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;

22
arch/s390/kernel/vtime.c
View 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;
}