time: track accurate idle time with tick_sched.idle_sleeptime

Current idle time in kstat is based on jiffies and is coarse grained.
tick_sched.idle_sleeptime is making some attempt to keep track of idle time
in a fine grained manner.  But, it is not handling the time spent in
interrupts fully.

Make tick_sched.idle_sleeptime accurate with respect to time spent on
handling interrupts and also add tick_sched.idle_lastupdate, which keeps
track of last time when idle_sleeptime was updated.

This statistics will be crucial for cpufreq-ondemand governor, which can
shed some conservative gaurd band that is uses today while setting the
frequency.  The ondemand changes that uses the exact idle time is coming
soon.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 8fe1ff40102d..d7837d45419e 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -280,9 +280,14 @@ asmlinkage void do_softirq(void)
  */
 void irq_enter(void)
 {
+#ifdef CONFIG_NO_HZ
+        int cpu = smp_processor_id();
+        if (idle_cpu(cpu) && !in_interrupt())
+                tick_nohz_stop_idle(cpu);
+#endif
         __irq_enter();
 #ifdef CONFIG_NO_HZ
-        if (idle_cpu(smp_processor_id()))
+        if (idle_cpu(cpu))
                 tick_nohz_update_jiffies();
 #endif
 }