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Commit f17fe85b authored by Steve Muckle's avatar Steve Muckle Committed by Syed Rameez Mustafa
Browse files

sched: tighten up jiffy to sched_clock mapping 



The tick code already tracks exact time a tick is expected
to arrive. This can be used to eliminate slack in the jiffy
to sched_clock mapping that aligns windows between a caller
of sched_set_window and the scheduler itself.

Change-Id: I9d47466658d01e6857d7457405459436d504a2ca
Signed-off-by: default avatarSteve Muckle <smuckle@codeaurora.org>
parent 4fe162d7

include/linux/tick.h

+1 −0
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ struct tick_sched { 


extern void __init tick_init(void);

extern int tick_is_oneshot_available(void);

extern u64 jiffy_to_sched_clock(u64 *now, u64 *jiffy_sched_clock);

extern struct tick_device *tick_get_device(int cpu);



# ifdef CONFIG_HIGH_RES_TIMERS

kernel/sched/core.c

+15 −15
Original line number Diff line number Diff line
@@ -1224,8 +1224,6 @@ __read_mostly unsigned int sched_ravg_window = 10000000; 
unsigned int __read_mostly sched_disable_window_stats;



static unsigned int sync_cpu;

static u64 sched_init_jiffy;

static u64 sched_clock_at_init_jiffy;



#define EXITING_TASK_MARKER	0xdeaddead
@@ -1897,23 +1895,16 @@ static inline void mark_task_starting(struct task_struct *p) 
	p->ravg.mark_start = wallclock;

}



static int update_alignment;



static inline void set_window_start(struct rq *rq)

{

	int cpu = cpu_of(rq);

	struct rq *sync_rq = cpu_rq(sync_cpu);



	if (cpu == sync_cpu && !update_alignment) {

		sched_init_jiffy = get_jiffies_64();

		sched_clock_at_init_jiffy = sched_clock();

	}



	if (rq->window_start || !sched_enable_hmp)

		return;



	if (cpu == sync_cpu) {

		rq->window_start = sched_clock_at_init_jiffy;

		rq->window_start = sched_clock();

	} else {

		raw_spin_unlock(&rq->lock);

		double_rq_lock(rq, sync_rq);
@@ -2140,20 +2131,29 @@ void sched_set_io_is_busy(int val) 


int sched_set_window(u64 window_start, unsigned int window_size)

{

	u64 ws, now;

	u64 now, cur_jiffies, jiffy_sched_clock;

	s64 ws;

	unsigned long flags;



	if (sched_use_pelt ||

		 (window_size * TICK_NSEC <  MIN_SCHED_RAVG_WINDOW))

			return -EINVAL;



	mutex_lock(&policy_mutex);

	update_alignment = 1;



	ws = (window_start - sched_init_jiffy); /* jiffy difference */

	/* Get a consistent view of sched_clock, jiffies, and the time

	 * since the last jiffy (based on last_jiffies_update). */

	local_irq_save(flags);

	cur_jiffies = jiffy_to_sched_clock(&now, &jiffy_sched_clock);

	local_irq_restore(flags);



	/* translate window_start from jiffies to nanoseconds */

	ws = (window_start - cur_jiffies); /* jiffy difference */

	ws *= TICK_NSEC;

	ws += sched_clock_at_init_jiffy;

	ws += jiffy_sched_clock;



	now = sched_clock();

	/* roll back calculated window start so that it is in

	 * the past (window stats must have a current window) */

	while (ws > now)

		ws -= (window_size * TICK_NSEC);

kernel/time/tick-sched.c

+32 −0
Original line number Diff line number Diff line
@@ -45,6 +45,38 @@ DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 
 */

static ktime_t last_jiffies_update;



/*

 * Conversion from ktime to sched_clock is error prone. Use this

 * as a safetly margin when calculating the sched_clock value at

 * a particular jiffy as last_jiffies_update uses ktime.

 */

#define SCHED_CLOCK_MARGIN 100000



static u64 ns_since_jiffy(void)

{

	ktime_t delta;



	delta = ktime_sub(ktime_get(), last_jiffies_update);



	return ktime_to_ns(delta);

}



u64 jiffy_to_sched_clock(u64 *now, u64 *jiffy_sched_clock)

{

	u64 cur_jiffies;

	unsigned long seq;



	do {

		seq = read_seqbegin(&jiffies_lock);

		*now = sched_clock();

		*jiffy_sched_clock = *now -

			(ns_since_jiffy() + SCHED_CLOCK_MARGIN);

		cur_jiffies = get_jiffies_64();

	} while (read_seqretry(&jiffies_lock, seq));



	return cur_jiffies;

}



struct tick_sched *tick_get_tick_sched(int cpu)

{

	return &per_cpu(tick_cpu_sched, cpu);