Commit 6378ddb5 authored by Venki Pallipadi's avatar Venki Pallipadi Committed by Ingo Molnar
Browse files

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: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent bbe4d18a

include/linux/tick.h

+6 −0
Original line number Diff line number Diff line
@@ -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

kernel/softirq.c

+6 −1
Original line number Diff line number Diff line
@@ -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

}

kernel/time/tick-sched.c

+48 −22
Original line number Diff line number Diff line
@@ -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

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