time: track accurate idle time with tick_sched.idle_sleeptime
Venki Pallipadi [Wed, 30 Jan 2008 12:30:04 +0000 (13:30 +0100)]
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>

include/linux/tick.h
kernel/softirq.c
kernel/time/tick-sched.c

index f4a1395..0fadf95 100644 (file)
@@ -51,8 +51,10 @@ struct tick_sched {
        unsigned long                   idle_jiffies;
        unsigned long                   idle_calls;
        unsigned long                   idle_sleeps;
+       int                             idle_active;
        ktime_t                         idle_entrytime;
        ktime_t                         idle_sleeptime;
+       ktime_t                         idle_lastupdate;
        ktime_t                         sleep_length;
        unsigned long                   last_jiffies;
        unsigned long                   next_jiffies;
@@ -103,6 +105,8 @@ extern void tick_nohz_stop_sched_tick(void);
 extern void tick_nohz_restart_sched_tick(void);
 extern void tick_nohz_update_jiffies(void);
 extern ktime_t tick_nohz_get_sleep_length(void);
+extern void tick_nohz_stop_idle(int cpu);
+extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 # else
 static inline void tick_nohz_stop_sched_tick(void) { }
 static inline void tick_nohz_restart_sched_tick(void) { }
@@ -113,6 +117,8 @@ static inline ktime_t tick_nohz_get_sleep_length(void)
 
        return len;
 }
+static inline void tick_nohz_stop_idle(int cpu) { }
+static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return 0; }
 # endif /* !NO_HZ */
 
 #endif
index 8fe1ff4..d7837d4 100644 (file)
@@ -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
 }
index 49e12f6..63f24b5 100644 (file)
@@ -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