[S390] /proc/stat idle field for idle cpus

The cpu idle field in the output of /proc/stat is too small for cpus
that have been idle for more than a tick. Add the architecture hook
arch_idle_time that allows to add the not accounted idle time of a
sleeping cpu without waking the cpu.

The s390 implementation of arch_idle_time uses the already existing
s390_idle_data per_cpu variable to find the sleep time of a neighboring
idle cpu.

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

2 files changed, 20 insertions, 0 deletions

diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index 95b0f7db3c6..941384fbd39 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -174,4 +174,8 @@ cputime64_to_clock_t(cputime64_t cputime)
        return __div(cputime, 4096000000ULL / USER_HZ);
 }
 
+cputime64_t s390_get_idle_time(int cpu);
+
+#define arch_idle_time(cpu) s390_get_idle_time(cpu)
+
 #endif /* _S390_CPUTIME_H */
diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 38ea92ff04f..c87f59bd824 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -240,6 +240,22 @@ void vtime_stop_cpu(void)
 	}
 }
 
+cputime64_t s390_get_idle_time(int cpu)
+{
+	struct s390_idle_data *idle;
+	unsigned long long now, idle_time, idle_enter;
+
+	idle = &per_cpu(s390_idle, cpu);
+	spin_lock(&idle->lock);
+	now = get_clock();
+	idle_time = 0;
+	idle_enter = idle->idle_enter;
+	if (idle_enter != 0ULL && idle_enter < now)
+		idle_time = now - idle_enter;
+	spin_unlock(&idle->lock);
+	return idle_time;
+}
+
 /*
  * Sorted add to a list. List is linear searched until first bigger
  * element is found.