/* *  kernel/sched/proc.c * *  Kernel load calculations, forked from sched/core.c */ #include <linux/export.h> #include "sched.h" unsigned long this_cpu_load(void){	struct rq *this = this_rq();	return this->cpu_load[0];}  /* * 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 nr_active, delta = 0; 	nr_active = this_rq->nr_running;	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 longcalc_load(unsigned long load, unsigned long exp, unsigned long active){	load *= exp;	load += active * (FIXED_1 - exp);	load += 1UL << (FSHIFT - 1);	return load >> FSHIFT;} #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 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_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_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) {		int idx = calc_load_write_idx();		atomic_long_add(delta, &calc_load_idle[idx]);	}} void calc_load_exit_idle(void){	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; 	/*	 * 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.	 */	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;} /** * 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 longfixed_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 longcalc_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_account_active(), but since an idle CPU folds its delta into * calc_load_tasks_idle per calc_load_account_idle(), all we need to do is fold * in the pending idle delta if our idle 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){	long delta, active, n; 	if (!time_before(jiffies, calc_load_update + 10)) {		/*		 * Catch-up, fold however many we are behind still		 */		delta = jiffies - calc_load_update - 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); 		calc_load_update += n * LOAD_FREQ;	} 	/*	 * Flip the idle 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_fold_idle(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. */void calc_global_load(unsigned long ticks){	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; 	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); 	calc_load_update += LOAD_FREQ; 	/*	 * In case we idled for multiple LOAD_FREQ intervals, catch up in bulk.	 */	calc_global_nohz();} /* * Called from update_cpu_load() to periodically update this CPU's * active count. */static void calc_load_account_active(struct rq *this_rq){	long delta; 	if (time_before(jiffies, this_rq->calc_load_update))		return; 	delta  = calc_load_fold_active(this_rq);	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 * * If a cpu misses updates for n-1 ticks (as it was idle) and update gets called * on nth tick when cpu may be busy, then we have: * load = ((2^idx - 1) / 2^idx)^(n-1) * load * load = (2^idx - 1) / 2^idx) * load + 1 / 2^idx * cur_load * * decay_load_missed() below does efficient calculation of * load = ((2^idx - 1) / 2^idx)^(n-1) * load * avoiding 0..n-1 loop doing load = ((2^idx - 1) / 2^idx) * load * * The calculation is approximated on a 128 point scale. * degrade_zero_ticks is the number of ticks after which load at any * particular idx is approximated to be zero. * degrade_factor is a precomputed table, a row for each load idx. * Each column corresponds to degradation factor for a power of two ticks, * based on 128 point scale. * Example: * row 2, col 3 (=12) says that the degradation at load idx 2 after * 8 ticks is 12/128 (which is an approximation of exact factor 3^8/4^8). * * With this power of 2 load factors, we can degrade the load n times * by looking at 1 bits in n and doing as many mult/shift instead of * n mult/shifts needed by the exact degradation. */#define DEGRADE_SHIFT		7static const unsigned char		degrade_zero_ticks[CPU_LOAD_IDX_MAX] = {0, 8, 32, 64, 128};static const unsigned char		degrade_factor[CPU_LOAD_IDX_MAX][DEGRADE_SHIFT + 1] = {					{0, 0, 0, 0, 0, 0, 0, 0},					{64, 32, 8, 0, 0, 0, 0, 0},					{96, 72, 40, 12, 1, 0, 0},					{112, 98, 75, 43, 15, 1, 0},					{120, 112, 98, 76, 45, 16, 2} }; /* * Update cpu_load for any missed ticks, due to tickless idle. The backlog * would be when CPU is idle and so we just decay the old load without * adding any new load. */static unsigned longdecay_load_missed(unsigned long load, unsigned long missed_updates, int idx){	int j = 0; 	if (!missed_updates)		return load; 	if (missed_updates >= degrade_zero_ticks[idx])		return 0; 	if (idx == 1)		return load >> missed_updates; 	while (missed_updates) {		if (missed_updates % 2)			load = (load * degrade_factor[idx][j]) >> DEGRADE_SHIFT; 		missed_updates >>= 1;		j++;	}	return load;} /* * Update rq->cpu_load[] statistics. This function is usually called every * scheduler tick (TICK_NSEC). With tickless idle this will not be called * every tick. We fix it up based on jiffies. */static void __update_cpu_load(struct rq *this_rq, unsigned long this_load,			      unsigned long pending_updates){	int i, scale; 	this_rq->nr_load_updates++; 	/* Update our load: */	this_rq->cpu_load[0] = this_load; /* Fasttrack for idx 0 */	for (i = 1, scale = 2; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {		unsigned long old_load, new_load; 		/* scale is effectively 1 << i now, and >> i divides by scale */ 		old_load = this_rq->cpu_load[i];		old_load = decay_load_missed(old_load, pending_updates - 1, i);		new_load = this_load;		/*		 * Round up the averaging division if load is increasing. This		 * prevents us from getting stuck on 9 if the load is 10, for		 * example.		 */		if (new_load > old_load)			new_load += scale - 1; 		this_rq->cpu_load[i] = (old_load * (scale - 1) + new_load) >> i;	} 

Lines 1–500 of 591. Load more