sched: Factor out load calculation code from sched/core.c --> sched/proc.c

This large chunk of load calculation code can be easily divorced
from the main core.c scheduler file, with only a couple
prototypes and externs added to a kernel/sched header.

Some recent commits expanded the code and the documentation of
it, making it large enough to warrant separation.  For example,
see:

  556061b, "sched/nohz: Fix rq->cpu_load[] calculations"
  5aaa0b7, "sched/nohz: Fix rq->cpu_load calculations some more"
  5167e8d, "sched/nohz: Rewrite and fix load-avg computation -- again"

More importantly, it helps reduce the size of the main
sched/core.c by yet another significant amount (~600 lines).

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1366398650-31599-2-git-send-email-paul.gortmaker@windriver.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 569 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 58453b8272fd..bfa7e77e0b50 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2056,575 +2056,6 @@ unsigned long nr_iowait_cpu(int cpu)
 	return atomic_read(&this->nr_iowait);
 }
 
-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 */
-static atomic_long_t calc_load_tasks;
-static 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;
-}
-
-static 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 long
-calc_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 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_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		7
-static 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 long
-decay_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;
-	}
-
-	sched_avg_update(this_rq);
-}
-
-#ifdef CONFIG_NO_HZ_COMMON
-/*
- * There is no sane way to deal with nohz on smp when using jiffies because the
- * cpu doing the jiffies update might drift wrt the cpu doing the jiffy reading
- * causing off-by-one errors in observed deltas; {0,2} instead of {1,1}.
- *
- * Therefore we cannot use the delta approach from the regular tick since that
- * would seriously skew the load calculation. However we'll make do for those
- * updates happening while idle (nohz_idle_balance) or coming out of idle
- * (tick_nohz_idle_exit).
- *
- * This means we might still be one tick off for nohz periods.
- */
-
-/*
- * Called from nohz_idle_balance() to update the load ratings before doing the
- * idle balance.
- */
-void update_idle_cpu_load(struct rq *this_rq)
-{
-	unsigned long curr_jiffies = ACCESS_ONCE(jiffies);
-	unsigned long load = this_rq->load.weight;
-	unsigned long pending_updates;
-
-	/*
-	 * bail if there's load or we're actually up-to-date.
-	 */
-	if (load || curr_jiffies == this_rq->last_load_update_tick)
-		return;
-
-	pending_updates = curr_jiffies - this_rq->last_load_update_tick;
-	this_rq->last_load_update_tick = curr_jiffies;
-
-	__update_cpu_load(this_rq, load, pending_updates);
-}
-
-/*
- * Called from tick_nohz_idle_exit() -- try and fix up the ticks we missed.
- */
-void update_cpu_load_nohz(void)
-{
-	struct rq *this_rq = this_rq();
-	unsigned long curr_jiffies = ACCESS_ONCE(jiffies);
-	unsigned long pending_updates;
-
-	if (curr_jiffies == this_rq->last_load_update_tick)
-		return;
-
-	raw_spin_lock(&this_rq->lock);
-	pending_updates = curr_jiffies - this_rq->last_load_update_tick;
-	if (pending_updates) {
-		this_rq->last_load_update_tick = curr_jiffies;
-		/*
-		 * We were idle, this means load 0, the current load might be
-		 * !0 due to remote wakeups and the sort.
-		 */
-		__update_cpu_load(this_rq, 0, pending_updates);
-	}
-	raw_spin_unlock(&this_rq->lock);
-}
-#endif /* CONFIG_NO_HZ_COMMON */
-
-/*
- * Called from scheduler_tick()
- */
-static void update_cpu_load_active(struct rq *this_rq)
-{
-	/*
-	 * See the mess around update_idle_cpu_load() / update_cpu_load_nohz().
-	 */
-	this_rq->last_load_update_tick = jiffies;
-	__update_cpu_load(this_rq, this_rq->load.weight, 1);
-
-	calc_load_account_active(this_rq);
-}
-
 #ifdef CONFIG_SMP
 
 /*