kernel/sched/loadavg.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * kernel/sched/loadavg.c
  *
  * This file contains the magic bits required to compute the global loadavg
  * figure. Its a silly number but people think its important. We go through
  * great pains to make it work on big machines and tickless kernels.
  */
 #include "sched.h"

 /*
  * 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 */
 atomic_long_t calc_load_tasks;
 unsigned long calc_load_update;
 unsigned long avenrun[3];
 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;
 }

 long calc_load_fold_active(struct rq *this_rq, long adjust)
 {
 	long nr_active, delta = 0;

 	nr_active = this_rq->nr_running - adjust;
 	nr_active += (long)this_rq->nr_uninterruptible;

 	if (nr_active != this_rq->calc_load_active) {
 		delta = nr_active - this_rq->calc_load_active;
 		this_rq->calc_load_active = nr_active;
 	}

 	return delta;
 }

 /*
  * a1 = a0 * e + a * (1 - e)
  */
 static unsigned long
 calc_load(unsigned long load, unsigned long exp, unsigned long active)
 {
 	unsigned long newload;

 	newload = load * exp + active * (FIXED_1 - exp);
 	if (active >= load)
 		newload += FIXED_1-1;

 	return newload / FIXED_1;
 }

 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * 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 NO_HZ-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 NO_HZ-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 NO_HZ contribution in this window while
  *    accumlating the new one.
  *
  *  - When we wake up from NO_HZ 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 NO_HZ-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 NO_HZ 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_nohz[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 NO_HZ-delta.
 	 */
 	if (!time_before(jiffies, READ_ONCE(calc_load_update)))
 		idx++;

 	return idx & 1;
 }

 static inline int calc_load_read_idx(void)
 {
 	return calc_load_idx & 1;
 }

 void calc_load_nohz_start(void)
 {
 	struct rq *this_rq = this_rq();
 	long delta;

 	/*
 	 * We're going into NO_HZ mode, if there's any pending delta, fold it
 	 * into the pending NO_HZ delta.
 	 */
 	delta = calc_load_fold_active(this_rq, 0);
 	if (delta) {
 		int idx = calc_load_write_idx();

 		atomic_long_add(delta, &calc_load_nohz[idx]);
 	}
 }

 void calc_load_nohz_stop(void)
 {
 	struct rq *this_rq = this_rq();

 	/*
 	 * If we're still before the pending sample window, we're done.
 	 */
 	this_rq->calc_load_update = READ_ONCE(calc_load_update);
 	if (time_before(jiffies, this_rq->calc_load_update))
 		return;

 	/*
 	 * 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 (time_before(jiffies, this_rq->calc_load_update + 10))
 		this_rq->calc_load_update += LOAD_FREQ;
 }

 static long calc_load_nohz_fold(void)
 {
 	int idx = calc_load_read_idx();
 	long delta = 0;

 	if (atomic_long_read(&calc_load_nohz[idx]))
 		delta = atomic_long_xchg(&calc_load_nohz[idx], 0);

 	return delta;
 }

 /**
  * fixed_power_int - compute: x^n, in O(log n) time
  *
  * @x:         base of the power
  * @frac_bits: fractional bits of @x
  * @n:         power to raise @x to.
  *
  * By exploiting the relation between the definition of the natural power
  * function: x^n := x*x*...*x (x multiplied by itself for n times), and
  * the binary encoding of numbers used by computers: n := \Sum n_i * 2^i,
  * (where: n_i \elem {0, 1}, the binary vector representing n),
  * we find: x^n := x^(\Sum n_i * 2^i) := \Prod x^(n_i * 2^i), which is
  * of course trivially computable in O(log_2 n), the length of our binary
  * vector.
  */
 static unsigned long
 fixed_power_int(unsigned long x, unsigned int frac_bits, unsigned int n)
 {
 	unsigned long result = 1UL << frac_bits;

 	if (n) {
 		for (;;) {
 			if (n & 1) {
 				result *= x;
 				result += 1UL << (frac_bits - 1);
 				result >>= frac_bits;
 			}
 			n >>= 1;
 			if (!n)
 				break;
 			x *= x;
 			x += 1UL << (frac_bits - 1);
 			x >>= frac_bits;
 		}
 	}

 	return result;
 }

 /*
  * a1 = a0 * e + a * (1 - e)
  *
  * a2 = a1 * e + a * (1 - e)
  *    = (a0 * e + a * (1 - e)) * e + a * (1 - e)
  *    = a0 * e^2 + a * (1 - e) * (1 + e)
  *
  * a3 = a2 * e + a * (1 - e)
  *    = (a0 * e^2 + a * (1 - e) * (1 + e)) * e + a * (1 - e)
  *    = a0 * e^3 + a * (1 - e) * (1 + e + e^2)
  *
  *  ...
  *
  * an = a0 * e^n + a * (1 - e) * (1 + e + ... + e^n-1) [1]
  *    = a0 * e^n + a * (1 - e) * (1 - e^n)/(1 - e)
  *    = a0 * e^n + a * (1 - e^n)
  *
  * [1] application of the geometric series:
  *
  *              n         1 - x^(n+1)
  *     S_n := \Sum x^i = -------------
  *             i=0          1 - x
  */
 static unsigned long
 calc_load_n(unsigned long load, unsigned long exp,
 	    unsigned long active, unsigned int n)
 {
 	return calc_load(load, fixed_power_int(exp, FSHIFT, n), active);
 }

 /*
  * NO_HZ can leave us missing all per-CPU ticks calling
  * calc_load_fold_active(), but since a NO_HZ CPU folds its delta into
  * calc_load_nohz per calc_load_nohz_start(), all we need to do is fold
  * in the pending NO_HZ delta if our NO_HZ period crossed a load cycle boundary.
  *
  * Once we've updated the global active value, we need to apply the exponential
  * weights adjusted to the number of cycles missed.
  */
 static void calc_global_nohz(void)
 {
 	unsigned long sample_window;
 	long delta, active, n;

 	sample_window = READ_ONCE(calc_load_update);
 	if (!time_before(jiffies, sample_window + 10)) {
 		/*
 		 * Catch-up, fold however many we are behind still
 		 */
 		delta = jiffies - sample_window - 10;
 		n = 1 + (delta / LOAD_FREQ);

 		active = atomic_long_read(&calc_load_tasks);
 		active = active > 0 ? active * FIXED_1 : 0;

 		avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n);
 		avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n);
 		avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n);

 		WRITE_ONCE(calc_load_update, sample_window + n * LOAD_FREQ);
 	}

 	/*
 	 * Flip the NO_HZ index...
 	 *
 	 * 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.
 	 */
 	smp_wmb();
 	calc_load_idx++;
 }
 #else /* !CONFIG_NO_HZ_COMMON */

 static inline long calc_load_nohz_fold(void) { return 0; }
 static inline void calc_global_nohz(void) { }

 #endif /* CONFIG_NO_HZ_COMMON */

 /*
  * calc_load - update the avenrun load estimates 10 ticks after the
  * CPUs have updated calc_load_tasks.
  *
  * Called from the global timer code.
  */
 void calc_global_load(unsigned long ticks)
 {
 	unsigned long sample_window;
 	long active, delta;

 	sample_window = READ_ONCE(calc_load_update);
 	if (time_before(jiffies, sample_window + 10))
 		return;

 	/*
 	 * Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs.
 	 */
 	delta = calc_load_nohz_fold();
 	if (delta)
 		atomic_long_add(delta, &calc_load_tasks);

 	active = atomic_long_read(&calc_load_tasks);
 	active = active > 0 ? active * FIXED_1 : 0;

 	avenrun[0] = calc_load(avenrun[0], EXP_1, active);
 	avenrun[1] = calc_load(avenrun[1], EXP_5, active);
 	avenrun[2] = calc_load(avenrun[2], EXP_15, active);

 	WRITE_ONCE(calc_load_update, sample_window + LOAD_FREQ);

 	/*
 	 * In case we went to NO_HZ for multiple LOAD_FREQ intervals
 	 * catch up in bulk.
 	 */
 	calc_global_nohz();
 }

 /*
  * Called from scheduler_tick() to periodically update this CPU's
  * active count.
  */
 void calc_global_load_tick(struct rq *this_rq)
 {
 	long delta;

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

 	delta  = calc_load_fold_active(this_rq, 0);
 	if (delta)
 		atomic_long_add(delta, &calc_load_tasks);

 	this_rq->calc_load_update += LOAD_FREQ;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* kernel/sched/loadavg.c
	*
	* This file contains the magic bits required to compute the global loadavg
	* figure. Its a silly number but people think its important. We go through
	* great pains to make it work on big machines and tickless kernels.
	*/
	#include "sched.h"

	/*
	* 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 */
	atomic_long_t calc_load_tasks;
	unsigned long calc_load_update;
	unsigned long avenrun[3];
	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;
	}

	long calc_load_fold_active(struct rq *this_rq, long adjust)
	{
	long nr_active, delta = 0;

	nr_active = this_rq->nr_running - adjust;
	nr_active += (long)this_rq->nr_uninterruptible;

	if (nr_active != this_rq->calc_load_active) {
	delta = nr_active - this_rq->calc_load_active;
	this_rq->calc_load_active = nr_active;
	}

	return delta;
	}

	/*
	* a1 = a0 * e + a * (1 - e)
	*/
	static unsigned long
	calc_load(unsigned long load, unsigned long exp, unsigned long active)
	{
	unsigned long newload;

	newload = load * exp + active * (FIXED_1 - exp);
	if (active >= load)
	newload += FIXED_1-1;

	return newload / FIXED_1;
	}

	#ifdef CONFIG_NO_HZ_COMMON
	/*
	* 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 NO_HZ-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 NO_HZ-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 NO_HZ contribution in this window while
	* accumlating the new one.
	*
	* - When we wake up from NO_HZ 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 NO_HZ-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 NO_HZ 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_nohz[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 NO_HZ-delta.
	*/
	if (!time_before(jiffies, READ_ONCE(calc_load_update)))
	idx++;

	return idx & 1;
	}

	static inline int calc_load_read_idx(void)
	{
	return calc_load_idx & 1;
	}

	void calc_load_nohz_start(void)
	{
	struct rq *this_rq = this_rq();
	long delta;

	/*
	* We're going into NO_HZ mode, if there's any pending delta, fold it
	* into the pending NO_HZ delta.
	*/
	delta = calc_load_fold_active(this_rq, 0);
	if (delta) {
	int idx = calc_load_write_idx();

	atomic_long_add(delta, &calc_load_nohz[idx]);
	}
	}

	void calc_load_nohz_stop(void)
	{
	struct rq *this_rq = this_rq();

	/*
	* If we're still before the pending sample window, we're done.
	*/
	this_rq->calc_load_update = READ_ONCE(calc_load_update);
	if (time_before(jiffies, this_rq->calc_load_update))
	return;

	/*
	* 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 (time_before(jiffies, this_rq->calc_load_update + 10))
	this_rq->calc_load_update += LOAD_FREQ;
	}

	static long calc_load_nohz_fold(void)
	{
	int idx = calc_load_read_idx();
	long delta = 0;

	if (atomic_long_read(&calc_load_nohz[idx]))
	delta = atomic_long_xchg(&calc_load_nohz[idx], 0);

	return delta;
	}

	/**
	* fixed_power_int - compute: x^n, in O(log n) time
	*
	* @x: base of the power
	* @frac_bits: fractional bits of @x
	* @n: power to raise @x to.
	*
	* By exploiting the relation between the definition of the natural power
	* function: x^n := xx...*x (x multiplied by itself for n times), and
	* the binary encoding of numbers used by computers: n := \Sum n_i * 2^i,
	* (where: n_i \elem {0, 1}, the binary vector representing n),
	* we find: x^n := x^(\Sum n_i * 2^i) := \Prod x^(n_i * 2^i), which is
	* of course trivially computable in O(log_2 n), the length of our binary
	* vector.
	*/
	static unsigned long
	fixed_power_int(unsigned long x, unsigned int frac_bits, unsigned int n)
	{
	unsigned long result = 1UL << frac_bits;

	if (n) {
	for (;;) {
	if (n & 1) {
	result *= x;
	result += 1UL << (frac_bits - 1);
	result >>= frac_bits;
	}
	n >>= 1;
	if (!n)
	break;
	x *= x;
	x += 1UL << (frac_bits - 1);
	x >>= frac_bits;
	}
	}

	return result;
	}

	/*
	* a1 = a0 * e + a * (1 - e)
	*
	* a2 = a1 * e + a * (1 - e)
	* = (a0 * e + a * (1 - e)) * e + a * (1 - e)
	* = a0 * e^2 + a * (1 - e) * (1 + e)
	*
	* a3 = a2 * e + a * (1 - e)
	* = (a0 * e^2 + a * (1 - e) * (1 + e)) * e + a * (1 - e)
	* = a0 * e^3 + a * (1 - e) * (1 + e + e^2)
	*
	* ...
	*
	* an = a0 * e^n + a * (1 - e) * (1 + e + ... + e^n-1) [1]
	* = a0 * e^n + a * (1 - e) * (1 - e^n)/(1 - e)
	* = a0 * e^n + a * (1 - e^n)
	*
	* [1] application of the geometric series:
	*
	* n 1 - x^(n+1)
	* S_n := \Sum x^i = -------------
	* i=0 1 - x
	*/
	static unsigned long
	calc_load_n(unsigned long load, unsigned long exp,
	unsigned long active, unsigned int n)
	{
	return calc_load(load, fixed_power_int(exp, FSHIFT, n), active);
	}

	/*
	* NO_HZ can leave us missing all per-CPU ticks calling
	* calc_load_fold_active(), but since a NO_HZ CPU folds its delta into
	* calc_load_nohz per calc_load_nohz_start(), all we need to do is fold
	* in the pending NO_HZ delta if our NO_HZ period crossed a load cycle boundary.
	*
	* Once we've updated the global active value, we need to apply the exponential
	* weights adjusted to the number of cycles missed.
	*/
	static void calc_global_nohz(void)
	{
	unsigned long sample_window;
	long delta, active, n;

	sample_window = READ_ONCE(calc_load_update);
	if (!time_before(jiffies, sample_window + 10)) {
	/*
	* Catch-up, fold however many we are behind still
	*/
	delta = jiffies - sample_window - 10;
	n = 1 + (delta / LOAD_FREQ);

	active = atomic_long_read(&calc_load_tasks);
	active = active > 0 ? active * FIXED_1 : 0;

	avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n);
	avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n);
	avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n);

	WRITE_ONCE(calc_load_update, sample_window + n * LOAD_FREQ);
	}

	/*
	* Flip the NO_HZ index...
	*
	* 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.
	*/
	smp_wmb();
	calc_load_idx++;
	}
	#else /* !CONFIG_NO_HZ_COMMON */

	static inline long calc_load_nohz_fold(void) { return 0; }
	static inline void calc_global_nohz(void) { }

	#endif /* CONFIG_NO_HZ_COMMON */

	/*
	* calc_load - update the avenrun load estimates 10 ticks after the
	* CPUs have updated calc_load_tasks.
	*
	* Called from the global timer code.
	*/
	void calc_global_load(unsigned long ticks)
	{
	unsigned long sample_window;
	long active, delta;

	sample_window = READ_ONCE(calc_load_update);
	if (time_before(jiffies, sample_window + 10))
	return;

	/*
	* Fold the 'old' NO_HZ-delta to include all NO_HZ CPUs.
	*/
	delta = calc_load_nohz_fold();
	if (delta)
	atomic_long_add(delta, &calc_load_tasks);

	active = atomic_long_read(&calc_load_tasks);
	active = active > 0 ? active * FIXED_1 : 0;

	avenrun[0] = calc_load(avenrun[0], EXP_1, active);
	avenrun[1] = calc_load(avenrun[1], EXP_5, active);
	avenrun[2] = calc_load(avenrun[2], EXP_15, active);

	WRITE_ONCE(calc_load_update, sample_window + LOAD_FREQ);

	/*
	* In case we went to NO_HZ for multiple LOAD_FREQ intervals
	* catch up in bulk.
	*/
	calc_global_nohz();
	}

	/*
	* Called from scheduler_tick() to periodically update this CPU's
	* active count.
	*/
	void calc_global_load_tick(struct rq *this_rq)
	{
	long delta;

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

	delta = calc_load_fold_active(this_rq, 0);
	if (delta)
	atomic_long_add(delta, &calc_load_tasks);

	this_rq->calc_load_update += LOAD_FREQ;
	}