sched/nohz: Rewrite and fix load-avg computation -- again

}

#endif

#ifdef CONFIG_NO_HZ

void calc_load_enter_idle(void);

void calc_load_exit_idle(void);

#else

static inline void calc_load_enter_idle(void) { }

static inline void calc_load_exit_idle(void) { }

#endif /* CONFIG_NO_HZ */

#ifndef CONFIG_CPUMASK_OFFSTACK

static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)

{

}

/*

 * Global load-average calculations

 *

 * We take a distributed and async approach to calculating the global load-avg

 * in order to minimize overhead.

 *

 * The global load average is an exponentially decaying average of nr_running +

 * nr_uninterruptible.

 *

 * Once every LOAD_FREQ:

 *

 *   nr_active = 0;

 *   for_each_possible_cpu(cpu)

 *   	nr_active += cpu_of(cpu)->nr_running + cpu_of(cpu)->nr_uninterruptible;

 *

 *   avenrun[n] = avenrun[0] * exp_n + nr_active * (1 - exp_n)

 *

 * Due to a number of reasons the above turns in the mess below:

 *

 *  - for_each_possible_cpu() is prohibitively expensive on machines with

 *    serious number of cpus, therefore we need to take a distributed approach

 *    to calculating nr_active.

 *

 *        \Sum_i x_i(t) = \Sum_i x_i(t) - x_i(t_0) | x_i(t_0) := 0

 *                      = \Sum_i { \Sum_j=1 x_i(t_j) - x_i(t_j-1) }

 *

 *    So assuming nr_active := 0 when we start out -- true per definition, we

 *    can simply take per-cpu deltas and fold those into a global accumulate

 *    to obtain the same result. See calc_load_fold_active().

 *

 *    Furthermore, in order to avoid synchronizing all per-cpu delta folding

 *    across the machine, we assume 10 ticks is sufficient time for every

 *    cpu to have completed this task.

 *

 *    This places an upper-bound on the IRQ-off latency of the machine. Then

 *    again, being late doesn't loose the delta, just wrecks the sample.

 *

 *  - cpu_rq()->nr_uninterruptible isn't accurately tracked per-cpu because

 *    this would add another cross-cpu cacheline miss and atomic operation

 *    to the wakeup path. Instead we increment on whatever cpu the task ran

 *    when it went into uninterruptible state and decrement on whatever cpu

 *    did the wakeup. This means that only the sum of nr_uninterruptible over

 *    all cpus yields the correct result.

 *

 *  This covers the NO_HZ=n code, for extra head-aches, see the comment below.

 */

/* Variables and functions for calc_load */

static atomic_long_t calc_load_tasks;

static unsigned long calc_load_update;

unsigned long avenrun[3];

EXPORT_SYMBOL(avenrun);

EXPORT_SYMBOL(avenrun); /* should be removed */

/**

 * get_avenrun - get the load average array

 * @loads:	pointer to dest load array

 * @offset:	offset to add

 * @shift:	shift count to shift the result left

 *

 * These values are estimates at best, so no need for locking.

 */

void get_avenrun(unsigned long *loads, unsigned long offset, int shift)

{

	loads[0] = (avenrun[0] + offset) << shift;

	loads[1] = (avenrun[1] + offset) << shift;

	loads[2] = (avenrun[2] + offset) << shift;

}

static long calc_load_fold_active(struct rq *this_rq)

{

	return delta;

}

/*

 * a1 = a0 * e + a * (1 - e)

 */

static unsigned long

calc_load(unsigned long load, unsigned long exp, unsigned long active)

{

#ifdef CONFIG_NO_HZ

/*

 * For NO_HZ we delay the active fold to the next LOAD_FREQ update.

 * Handle NO_HZ for the global load-average.

 *

 * Since the above described distributed algorithm to compute the global

 * load-average relies on per-cpu sampling from the tick, it is affected by

 * NO_HZ.

 *

 * The basic idea is to fold the nr_active delta into a global idle-delta upon

 * entering NO_HZ state such that we can include this as an 'extra' cpu delta

 * when we read the global state.

 *

 * Obviously reality has to ruin such a delightfully simple scheme:

 *

 *  - When we go NO_HZ idle during the window, we can negate our sample

 *    contribution, causing under-accounting.

 *

 *    We avoid this by keeping two idle-delta counters and flipping them

 *    when the window starts, thus separating old and new NO_HZ load.

 *

 *    The only trick is the slight shift in index flip for read vs write.

 *

 *        0s            5s            10s           15s

 *          +10           +10           +10           +10

 *        |-|-----------|-|-----------|-|-----------|-|

 *    r:0 0 1           1 0           0 1           1 0

 *    w:0 1 1           0 0           1 1           0 0

 *

 *    This ensures we'll fold the old idle contribution in this window while

 *    accumlating the new one.

 *

 *  - When we wake up from NO_HZ idle during the window, we push up our

 *    contribution, since we effectively move our sample point to a known

 *    busy state.

 *

 *    This is solved by pushing the window forward, and thus skipping the

 *    sample, for this cpu (effectively using the idle-delta for this cpu which

 *    was in effect at the time the window opened). This also solves the issue

 *    of having to deal with a cpu having been in NOHZ idle for multiple

 *    LOAD_FREQ intervals.

 *

 * When making the ILB scale, we should try to pull this in as well.

 */

static atomic_long_t calc_load_tasks_idle;

static atomic_long_t calc_load_idle[2];

static int calc_load_idx;

static inline int calc_load_write_idx(void)

{

	int idx = calc_load_idx;

	/*

	 * See calc_global_nohz(), if we observe the new index, we also

	 * need to observe the new update time.

	 */

	smp_rmb();

	/*

	 * If the folding window started, make sure we start writing in the

	 * next idle-delta.

	 */

	if (!time_before(jiffies, calc_load_update))

		idx++;

	return idx & 1;

}

static inline int calc_load_read_idx(void)

{

	return calc_load_idx & 1;

}

void calc_load_account_idle(struct rq *this_rq)

void calc_load_enter_idle(void)

{

	struct rq *this_rq = this_rq();

	long delta;

	/*

	 * We're going into NOHZ mode, if there's any pending delta, fold it

	 * into the pending idle delta.

	 */

	delta = calc_load_fold_active(this_rq);

	if (delta)

		atomic_long_add(delta, &calc_load_tasks_idle);

	if (delta) {

		int idx = calc_load_write_idx();

		atomic_long_add(delta, &calc_load_idle[idx]);

	}

}

static long calc_load_fold_idle(void)

void calc_load_exit_idle(void)

{

	long delta = 0;

	struct rq *this_rq = this_rq();

	/*

	 * If we're still before the sample window, we're done.

	 */

	if (time_before(jiffies, this_rq->calc_load_update))

		return;

	/*

	 * Its got a race, we don't care...

	 * We woke inside or after the sample window, this means we're already

	 * accounted through the nohz accounting, so skip the entire deal and

	 * sync up for the next window.

	 */

	if (atomic_long_read(&calc_load_tasks_idle))

		delta = atomic_long_xchg(&calc_load_tasks_idle, 0);

	this_rq->calc_load_update = calc_load_update;

	if (time_before(jiffies, this_rq->calc_load_update + 10))

		this_rq->calc_load_update += LOAD_FREQ;

}

static long calc_load_fold_idle(void)

{

	int idx = calc_load_read_idx();

	long delta = 0;

	if (atomic_long_read(&calc_load_idle[idx]))

		delta = atomic_long_xchg(&calc_load_idle[idx], 0);

	return delta;

}

{

	long delta, active, n;

	/*

	 * If we crossed a calc_load_update boundary, make sure to fold

	 * any pending idle changes, the respective CPUs might have

	 * missed the tick driven calc_load_account_active() update

	 * due to NO_HZ.

	 */

	delta = calc_load_fold_idle();

	if (delta)

		atomic_long_add(delta, &calc_load_tasks);

	/*

	 * It could be the one fold was all it took, we done!

	 */

	if (time_before(jiffies, calc_load_update + 10))

		return;

	if (!time_before(jiffies, calc_load_update + 10)) {

		/*

		 * Catch-up, fold however many we are behind still

		 */

		calc_load_update += n * LOAD_FREQ;

	}

#else

void calc_load_account_idle(struct rq *this_rq)

{

}

static inline long calc_load_fold_idle(void)

{

	return 0;

}

static void calc_global_nohz(void)

{

}

#endif

/**

 * get_avenrun - get the load average array

 * @loads:	pointer to dest load array

 * @offset:	offset to add

 * @shift:	shift count to shift the result left

	/*

	 * Flip the idle index...

	 *

 * These values are estimates at best, so no need for locking.

	 * Make sure we first write the new time then flip the index, so that

	 * calc_load_write_idx() will see the new time when it reads the new

	 * index, this avoids a double flip messing things up.

	 */

void get_avenrun(unsigned long *loads, unsigned long offset, int shift)

{

	loads[0] = (avenrun[0] + offset) << shift;

	loads[1] = (avenrun[1] + offset) << shift;

	loads[2] = (avenrun[2] + offset) << shift;

	smp_wmb();

	calc_load_idx++;

}

#else /* !CONFIG_NO_HZ */

static inline long calc_load_fold_idle(void) { return 0; }

static inline void calc_global_nohz(void) { }

#endif /* CONFIG_NO_HZ */

/*

 * calc_load - update the avenrun load estimates 10 ticks after the

 */

void calc_global_load(unsigned long ticks)

{

	long active;

	long active, delta;

	if (time_before(jiffies, calc_load_update + 10))

		return;

	/*

	 * Fold the 'old' idle-delta to include all NO_HZ cpus.

	 */

	delta = calc_load_fold_idle();

	if (delta)

		atomic_long_add(delta, &calc_load_tasks);

	active = atomic_long_read(&calc_load_tasks);

	active = active > 0 ? active * FIXED_1 : 0;

	calc_load_update += LOAD_FREQ;

	/*

	 * Account one period with whatever state we found before

	 * folding in the nohz state and ageing the entire idle period.

	 *

	 * This avoids loosing a sample when we go idle between 

	 * calc_load_account_active() (10 ticks ago) and now and thus

	 * under-accounting.

	 * In case we idled for multiple LOAD_FREQ intervals, catch up in bulk.

	 */

	calc_global_nohz();

}

		return;

	delta  = calc_load_fold_active(this_rq);

	delta += calc_load_fold_idle();

	if (delta)

		atomic_long_add(delta, &calc_load_tasks);

	this_rq->calc_load_update += LOAD_FREQ;

}

/*

 * End of global load-average stuff

 */

/*

 * The exact cpuload at various idx values, calculated at every tick would be

 * load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load

static struct task_struct *pick_next_task_idle(struct rq *rq)

{

	schedstat_inc(rq, sched_goidle);

	calc_load_account_idle(rq);

	return rq->idle;

}

	return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;

}

void calc_load_account_idle(struct rq *this_rq);

#ifdef CONFIG_SCHED_HRTICK

/*

		 */

		if (!ts->tick_stopped) {

			select_nohz_load_balancer(1);

			calc_load_enter_idle();

			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);

			ts->tick_stopped = 1;

		account_idle_ticks(ticks);

#endif

	calc_load_exit_idle();

	touch_softlockup_watchdog();

	/*

	 * Cancel the scheduled timer and restore the tick