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>

2 files changed, 54 insertions, 23 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
 }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 49e12f6a4bab..63f24b550695 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -143,6 +143,44 @@ void tick_nohz_update_jiffies(void)
         local_irq_restore(flags);
 }
 
+void tick_nohz_stop_idle(int cpu)
+{
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+        if (ts->idle_active) {
+                ktime_t now, delta;
+                now = ktime_get();
+                delta = ktime_sub(now, ts->idle_entrytime);
+                ts->idle_lastupdate = now;
+                ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+                ts->idle_active = 0;
+        }
+}
+
+static ktime_t tick_nohz_start_idle(int cpu)
+{
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+        ktime_t now, delta;
+
+        now = ktime_get();
+        if (ts->idle_active) {
+                delta = ktime_sub(now, ts->idle_entrytime);
+                ts->idle_lastupdate = now;
+                ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
+        }
+        ts->idle_entrytime = now;
+        ts->idle_active = 1;
+        return now;
+}
+
+u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
+{
+        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+        *last_update_time = ktime_to_us(ts->idle_lastupdate);
+        return ktime_to_us(ts->idle_sleeptime);
+}
+
 /**
  * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
  *
@@ -155,13 +193,14 @@ void tick_nohz_stop_sched_tick(void)
         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
         unsigned long rt_jiffies;
         struct tick_sched *ts;
-        ktime_t last_update, expires, now, delta;
+        ktime_t last_update, expires, now;
         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
         int cpu;
 
         local_irq_save(flags);
 
         cpu = smp_processor_id();
+        now = tick_nohz_start_idle(cpu);
         ts = &per_cpu(tick_cpu_sched, cpu);
 
         /*
@@ -193,19 +232,7 @@ void tick_nohz_stop_sched_tick(void)
                 }
         }
 
-        now = ktime_get();
-        /*
-         * When called from irq_exit we need to account the idle sleep time
-         * correctly.
-         */
-        if (ts->tick_stopped) {
-                delta = ktime_sub(now, ts->idle_entrytime);
-                ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
-        }
-
-        ts->idle_entrytime = now;
         ts->idle_calls++;
-
         /* Read jiffies and the time when jiffies were updated last */
         do {
                 seq = read_seqbegin(&xtime_lock);
@@ -337,23 +364,22 @@ void tick_nohz_restart_sched_tick(void)
         int cpu = smp_processor_id();
         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
         unsigned long ticks;
-        ktime_t now, delta;
+        ktime_t now;
 
-        if (!ts->tick_stopped)
+        local_irq_disable();
+        tick_nohz_stop_idle(cpu);
+
+        if (!ts->tick_stopped) {
+                local_irq_enable();
                 return;
+        }
 
         /* Update jiffies first */
-        now = ktime_get();
-
-        local_irq_disable();
         select_nohz_load_balancer(0);
+        now = ktime_get();
         tick_do_update_jiffies64(now);
         cpu_clear(cpu, nohz_cpu_mask);
 
-        /* Account the idle time */
-        delta = ktime_sub(now, ts->idle_entrytime);
-        ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
-
         /*
          * We stopped the tick in idle. Update process times would miss the
          * time we slept as update_process_times does only a 1 tick