forked from Minki/linux
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>
This commit is contained in:
Paul Gortmaker
Ingo Molnar
parent
534c97b095
commit
45ceebf776
@ -11,7 +11,7 @@ ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
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CFLAGS_core.o := $(PROFILING) -fno-omit-frame-pointer
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endif
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obj-y += core.o clock.o cputime.o idle_task.o fair.o rt.o stop_task.o
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obj-y += core.o proc.o clock.o cputime.o idle_task.o fair.o rt.o stop_task.o
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obj-$(CONFIG_SMP) += cpupri.o
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obj-$(CONFIG_SCHED_AUTOGROUP) += auto_group.o
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obj-$(CONFIG_SCHEDSTATS) += stats.o
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@ -2056,575 +2056,6 @@ unsigned long nr_iowait_cpu(int cpu)
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return atomic_read(&this->nr_iowait);
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}
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unsigned long this_cpu_load(void)
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{
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struct rq *this = this_rq();
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return this->cpu_load[0];
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}
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/*
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* Global load-average calculations
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*
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* We take a distributed and async approach to calculating the global load-avg
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* in order to minimize overhead.
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*
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* The global load average is an exponentially decaying average of nr_running +
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* nr_uninterruptible.
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*
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* Once every LOAD_FREQ:
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*
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* nr_active = 0;
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* for_each_possible_cpu(cpu)
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* nr_active += cpu_of(cpu)->nr_running + cpu_of(cpu)->nr_uninterruptible;
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*
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* avenrun[n] = avenrun[0] * exp_n + nr_active * (1 - exp_n)
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*
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* Due to a number of reasons the above turns in the mess below:
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*
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* - for_each_possible_cpu() is prohibitively expensive on machines with
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* serious number of cpus, therefore we need to take a distributed approach
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* to calculating nr_active.
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*
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* \Sum_i x_i(t) = \Sum_i x_i(t) - x_i(t_0) | x_i(t_0) := 0
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* = \Sum_i { \Sum_j=1 x_i(t_j) - x_i(t_j-1) }
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*
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* So assuming nr_active := 0 when we start out -- true per definition, we
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* can simply take per-cpu deltas and fold those into a global accumulate
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* to obtain the same result. See calc_load_fold_active().
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*
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* Furthermore, in order to avoid synchronizing all per-cpu delta folding
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* across the machine, we assume 10 ticks is sufficient time for every
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* cpu to have completed this task.
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*
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* This places an upper-bound on the IRQ-off latency of the machine. Then
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* again, being late doesn't loose the delta, just wrecks the sample.
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*
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* - cpu_rq()->nr_uninterruptible isn't accurately tracked per-cpu because
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* this would add another cross-cpu cacheline miss and atomic operation
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* to the wakeup path. Instead we increment on whatever cpu the task ran
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* when it went into uninterruptible state and decrement on whatever cpu
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* did the wakeup. This means that only the sum of nr_uninterruptible over
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* all cpus yields the correct result.
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*
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* This covers the NO_HZ=n code, for extra head-aches, see the comment below.
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*/
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/* Variables and functions for calc_load */
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static atomic_long_t calc_load_tasks;
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static unsigned long calc_load_update;
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unsigned long avenrun[3];
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EXPORT_SYMBOL(avenrun); /* should be removed */
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/**
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* get_avenrun - get the load average array
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* @loads: pointer to dest load array
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* @offset: offset to add
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* @shift: shift count to shift the result left
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*
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* These values are estimates at best, so no need for locking.
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*/
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void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
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{
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loads[0] = (avenrun[0] + offset) << shift;
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loads[1] = (avenrun[1] + offset) << shift;
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loads[2] = (avenrun[2] + offset) << shift;
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}
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static long calc_load_fold_active(struct rq *this_rq)
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{
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long nr_active, delta = 0;
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nr_active = this_rq->nr_running;
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nr_active += (long) this_rq->nr_uninterruptible;
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if (nr_active != this_rq->calc_load_active) {
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delta = nr_active - this_rq->calc_load_active;
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this_rq->calc_load_active = nr_active;
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}
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return delta;
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}
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/*
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* a1 = a0 * e + a * (1 - e)
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*/
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static unsigned long
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calc_load(unsigned long load, unsigned long exp, unsigned long active)
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{
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load *= exp;
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load += active * (FIXED_1 - exp);
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load += 1UL << (FSHIFT - 1);
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return load >> FSHIFT;
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}
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#ifdef CONFIG_NO_HZ_COMMON
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/*
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* Handle NO_HZ for the global load-average.
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*
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* Since the above described distributed algorithm to compute the global
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* load-average relies on per-cpu sampling from the tick, it is affected by
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* NO_HZ.
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*
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* The basic idea is to fold the nr_active delta into a global idle-delta upon
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* entering NO_HZ state such that we can include this as an 'extra' cpu delta
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* when we read the global state.
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*
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* Obviously reality has to ruin such a delightfully simple scheme:
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*
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* - When we go NO_HZ idle during the window, we can negate our sample
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* contribution, causing under-accounting.
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*
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* We avoid this by keeping two idle-delta counters and flipping them
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* when the window starts, thus separating old and new NO_HZ load.
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*
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* The only trick is the slight shift in index flip for read vs write.
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*
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* 0s 5s 10s 15s
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* +10 +10 +10 +10
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* |-|-----------|-|-----------|-|-----------|-|
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* r:0 0 1 1 0 0 1 1 0
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* w:0 1 1 0 0 1 1 0 0
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*
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* This ensures we'll fold the old idle contribution in this window while
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* accumlating the new one.
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*
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* - When we wake up from NO_HZ idle during the window, we push up our
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* contribution, since we effectively move our sample point to a known
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* busy state.
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*
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* This is solved by pushing the window forward, and thus skipping the
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* sample, for this cpu (effectively using the idle-delta for this cpu which
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* was in effect at the time the window opened). This also solves the issue
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* of having to deal with a cpu having been in NOHZ idle for multiple
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* LOAD_FREQ intervals.
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*
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* When making the ILB scale, we should try to pull this in as well.
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*/
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static atomic_long_t calc_load_idle[2];
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static int calc_load_idx;
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static inline int calc_load_write_idx(void)
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{
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int idx = calc_load_idx;
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/*
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* See calc_global_nohz(), if we observe the new index, we also
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* need to observe the new update time.
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*/
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smp_rmb();
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/*
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* If the folding window started, make sure we start writing in the
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* next idle-delta.
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*/
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if (!time_before(jiffies, calc_load_update))
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idx++;
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return idx & 1;
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}
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static inline int calc_load_read_idx(void)
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{
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return calc_load_idx & 1;
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}
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void calc_load_enter_idle(void)
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{
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struct rq *this_rq = this_rq();
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long delta;
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/*
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* We're going into NOHZ mode, if there's any pending delta, fold it
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* into the pending idle delta.
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*/
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delta = calc_load_fold_active(this_rq);
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if (delta) {
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int idx = calc_load_write_idx();
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atomic_long_add(delta, &calc_load_idle[idx]);
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}
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}
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void calc_load_exit_idle(void)
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{
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struct rq *this_rq = this_rq();
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/*
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* If we're still before the sample window, we're done.
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*/
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if (time_before(jiffies, this_rq->calc_load_update))
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return;
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/*
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* We woke inside or after the sample window, this means we're already
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* accounted through the nohz accounting, so skip the entire deal and
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* sync up for the next window.
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*/
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this_rq->calc_load_update = calc_load_update;
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if (time_before(jiffies, this_rq->calc_load_update + 10))
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this_rq->calc_load_update += LOAD_FREQ;
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}
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static long calc_load_fold_idle(void)
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{
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int idx = calc_load_read_idx();
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long delta = 0;
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if (atomic_long_read(&calc_load_idle[idx]))
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delta = atomic_long_xchg(&calc_load_idle[idx], 0);
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return delta;
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}
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/**
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* fixed_power_int - compute: x^n, in O(log n) time
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*
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* @x: base of the power
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* @frac_bits: fractional bits of @x
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* @n: power to raise @x to.
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*
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* By exploiting the relation between the definition of the natural power
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* function: x^n := x*x*...*x (x multiplied by itself for n times), and
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* the binary encoding of numbers used by computers: n := \Sum n_i * 2^i,
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* (where: n_i \elem {0, 1}, the binary vector representing n),
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* we find: x^n := x^(\Sum n_i * 2^i) := \Prod x^(n_i * 2^i), which is
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* of course trivially computable in O(log_2 n), the length of our binary
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* vector.
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*/
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static unsigned long
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fixed_power_int(unsigned long x, unsigned int frac_bits, unsigned int n)
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{
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unsigned long result = 1UL << frac_bits;
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if (n) for (;;) {
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if (n & 1) {
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result *= x;
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result += 1UL << (frac_bits - 1);
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result >>= frac_bits;
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}
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n >>= 1;
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if (!n)
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break;
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x *= x;
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x += 1UL << (frac_bits - 1);
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x >>= frac_bits;
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}
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return result;
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}
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/*
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* a1 = a0 * e + a * (1 - e)
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*
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* a2 = a1 * e + a * (1 - e)
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* = (a0 * e + a * (1 - e)) * e + a * (1 - e)
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* = a0 * e^2 + a * (1 - e) * (1 + e)
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*
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* a3 = a2 * e + a * (1 - e)
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* = (a0 * e^2 + a * (1 - e) * (1 + e)) * e + a * (1 - e)
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* = a0 * e^3 + a * (1 - e) * (1 + e + e^2)
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*
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* ...
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*
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* an = a0 * e^n + a * (1 - e) * (1 + e + ... + e^n-1) [1]
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* = a0 * e^n + a * (1 - e) * (1 - e^n)/(1 - e)
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* = a0 * e^n + a * (1 - e^n)
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*
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* [1] application of the geometric series:
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*
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* n 1 - x^(n+1)
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* S_n := \Sum x^i = -------------
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* i=0 1 - x
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*/
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static unsigned long
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calc_load_n(unsigned long load, unsigned long exp,
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unsigned long active, unsigned int n)
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{
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return calc_load(load, fixed_power_int(exp, FSHIFT, n), active);
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}
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/*
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* NO_HZ can leave us missing all per-cpu ticks calling
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* calc_load_account_active(), but since an idle CPU folds its delta into
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* calc_load_tasks_idle per calc_load_account_idle(), all we need to do is fold
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* in the pending idle delta if our idle period crossed a load cycle boundary.
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*
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* Once we've updated the global active value, we need to apply the exponential
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* weights adjusted to the number of cycles missed.
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*/
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static void calc_global_nohz(void)
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{
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long delta, active, n;
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if (!time_before(jiffies, calc_load_update + 10)) {
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/*
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* Catch-up, fold however many we are behind still
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*/
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delta = jiffies - calc_load_update - 10;
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n = 1 + (delta / LOAD_FREQ);
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active = atomic_long_read(&calc_load_tasks);
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active = active > 0 ? active * FIXED_1 : 0;
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avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n);
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avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n);
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avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n);
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calc_load_update += n * LOAD_FREQ;
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}
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/*
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* Flip the idle index...
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*
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* Make sure we first write the new time then flip the index, so that
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* calc_load_write_idx() will see the new time when it reads the new
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* index, this avoids a double flip messing things up.
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*/
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smp_wmb();
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calc_load_idx++;
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}
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#else /* !CONFIG_NO_HZ_COMMON */
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static inline long calc_load_fold_idle(void) { return 0; }
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static inline void calc_global_nohz(void) { }
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#endif /* CONFIG_NO_HZ_COMMON */
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/*
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* calc_load - update the avenrun load estimates 10 ticks after the
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* CPUs have updated calc_load_tasks.
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*/
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void calc_global_load(unsigned long ticks)
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{
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long active, delta;
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if (time_before(jiffies, calc_load_update + 10))
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return;
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/*
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* Fold the 'old' idle-delta to include all NO_HZ cpus.
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*/
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delta = calc_load_fold_idle();
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if (delta)
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atomic_long_add(delta, &calc_load_tasks);
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active = atomic_long_read(&calc_load_tasks);
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active = active > 0 ? active * FIXED_1 : 0;
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avenrun[0] = calc_load(avenrun[0], EXP_1, active);
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avenrun[1] = calc_load(avenrun[1], EXP_5, active);
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avenrun[2] = calc_load(avenrun[2], EXP_15, active);
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calc_load_update += LOAD_FREQ;
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/*
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* In case we idled for multiple LOAD_FREQ intervals, catch up in bulk.
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*/
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calc_global_nohz();
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}
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/*
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* Called from update_cpu_load() to periodically update this CPU's
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* active count.
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*/
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static void calc_load_account_active(struct rq *this_rq)
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{
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long delta;
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if (time_before(jiffies, this_rq->calc_load_update))
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return;
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delta = calc_load_fold_active(this_rq);
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if (delta)
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atomic_long_add(delta, &calc_load_tasks);
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this_rq->calc_load_update += LOAD_FREQ;
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}
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/*
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* End of global load-average stuff
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*/
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/*
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* The exact cpuload at various idx values, calculated at every tick would be
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* load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load
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*
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* If a cpu misses updates for n-1 ticks (as it was idle) and update gets called
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* on nth tick when cpu may be busy, then we have:
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* load = ((2^idx - 1) / 2^idx)^(n-1) * load
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* load = (2^idx - 1) / 2^idx) * load + 1 / 2^idx * cur_load
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*
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* decay_load_missed() below does efficient calculation of
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* load = ((2^idx - 1) / 2^idx)^(n-1) * load
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* avoiding 0..n-1 loop doing load = ((2^idx - 1) / 2^idx) * load
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*
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* The calculation is approximated on a 128 point scale.
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* degrade_zero_ticks is the number of ticks after which load at any
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* particular idx is approximated to be zero.
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* degrade_factor is a precomputed table, a row for each load idx.
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* Each column corresponds to degradation factor for a power of two ticks,
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* based on 128 point scale.
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* Example:
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* row 2, col 3 (=12) says that the degradation at load idx 2 after
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* 8 ticks is 12/128 (which is an approximation of exact factor 3^8/4^8).
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*
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* With this power of 2 load factors, we can degrade the load n times
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* by looking at 1 bits in n and doing as many mult/shift instead of
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* n mult/shifts needed by the exact degradation.
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*/
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#define DEGRADE_SHIFT 7
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static const unsigned char
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degrade_zero_ticks[CPU_LOAD_IDX_MAX] = {0, 8, 32, 64, 128};
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static const unsigned char
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degrade_factor[CPU_LOAD_IDX_MAX][DEGRADE_SHIFT + 1] = {
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{0, 0, 0, 0, 0, 0, 0, 0},
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{64, 32, 8, 0, 0, 0, 0, 0},
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{96, 72, 40, 12, 1, 0, 0},
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{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
|
||||
|
||||
/*
|
||||
|
||||
578
kernel/sched/proc.c
Normal file
578
kernel/sched/proc.c
Normal file
@ -0,0 +1,578 @@
|
||||
/*
|
||||
* 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 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 */
|
||||
|
||||
/*
|
||||
* Called from scheduler_tick()
|
||||
*/
|
||||
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);
|
||||
}
|
||||
@ -10,8 +10,16 @@
|
||||
#include "cpupri.h"
|
||||
#include "cpuacct.h"
|
||||
|
||||
struct rq;
|
||||
|
||||
extern __read_mostly int scheduler_running;
|
||||
|
||||
extern unsigned long calc_load_update;
|
||||
extern atomic_long_t calc_load_tasks;
|
||||
|
||||
extern long calc_load_fold_active(struct rq *this_rq);
|
||||
extern void update_cpu_load_active(struct rq *this_rq);
|
||||
|
||||
/*
|
||||
* Convert user-nice values [ -20 ... 0 ... 19 ]
|
||||
* to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
|
||||
|
||||
Loading…
Reference in New Issue
Block a user