[PATCH] improve precision of idle time detection.

Increase the precision of the idle time calculation that is exported
to user space via /sys/devices/system/cpu/cpu<x>/idle_time_us

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

1 files changed, 13 insertions, 12 deletions

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 6fc78541dc57..3979a6fc0882 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -851,9 +851,11 @@ static ssize_t show_idle_count(struct sys_device *dev,
         unsigned long long idle_count;
 
         idle = &per_cpu(s390_idle, dev->id);
-        spin_lock_irq(&idle->lock);
+        spin_lock(&idle->lock);
         idle_count = idle->idle_count;
-        spin_unlock_irq(&idle->lock);
+        if (idle->idle_enter)
+                idle_count++;
+        spin_unlock(&idle->lock);
         return sprintf(buf, "%llu\n", idle_count);
 }
 static SYSDEV_ATTR(idle_count, 0444, show_idle_count, NULL);
@@ -862,18 +864,17 @@ static ssize_t show_idle_time(struct sys_device *dev,
                                 struct sysdev_attribute *attr, char *buf)
 {
         struct s390_idle_data *idle;
-        unsigned long long new_time;
+        unsigned long long now, idle_time, idle_enter;
 
         idle = &per_cpu(s390_idle, dev->id);
-        spin_lock_irq(&idle->lock);
-        if (idle->in_idle) {
-                new_time = get_clock();
-                idle->idle_time += new_time - idle->idle_enter;
-                idle->idle_enter = new_time;
-        }
-        new_time = idle->idle_time;
-        spin_unlock_irq(&idle->lock);
-        return sprintf(buf, "%llu\n", new_time >> 12);
+        spin_lock(&idle->lock);
+        now = get_clock();
+        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);
+        return sprintf(buf, "%llu\n", idle_time >> 12);
 }
 static SYSDEV_ATTR(idle_time_us, 0444, show_idle_time, NULL);