sched: fair: weight calculations
In order to level the hierarchy, we need to calculate load based on the
root view. That is, each task's load is in the same unit.
A
/ \
B 1
/ \
2 3
To compute 1's load we do:
weight(1)
--------------
rq_weight(A)
To compute 2's load we do:
weight(2) weight(B)
------------ * -----------
rq_weight(B) rw_weight(A)
This yields load fractions in comparable units.
The consequence is that it changes virtual time. We used to have:
time_{i}
vtime_{i} = ------------
weight_{i}
vtime = \Sum vtime_{i} = time / rq_weight.
But with the new way of load calculation we get that vtime equals time.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
Ingo Molnar
parent
4a55bd5e97
commit
8f1bc385cf
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@ -1320,6 +1320,9 @@ static void __resched_task(struct task_struct *p, int tif_bit)
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*/
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#define SRR(x, y) (((x) + (1UL << ((y) - 1))) >> (y))
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/*
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* delta *= weight / lw
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*/
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static unsigned long
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calc_delta_mine(unsigned long delta_exec, unsigned long weight,
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struct load_weight *lw)
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@ -1342,12 +1345,6 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
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return (unsigned long)min(tmp, (u64)(unsigned long)LONG_MAX);
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}
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static inline unsigned long
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calc_delta_fair(unsigned long delta_exec, struct load_weight *lw)
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{
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return calc_delta_mine(delta_exec, NICE_0_LOAD, lw);
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}
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static inline void update_load_add(struct load_weight *lw, unsigned long inc)
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{
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lw->weight += inc;
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@ -333,6 +333,34 @@ int sched_nr_latency_handler(struct ctl_table *table, int write,
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}
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#endif
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/*
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* delta *= w / rw
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*/
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static inline unsigned long
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calc_delta_weight(unsigned long delta, struct sched_entity *se)
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{
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for_each_sched_entity(se) {
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delta = calc_delta_mine(delta,
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se->load.weight, &cfs_rq_of(se)->load);
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}
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return delta;
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}
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/*
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* delta *= rw / w
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*/
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static inline unsigned long
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calc_delta_fair(unsigned long delta, struct sched_entity *se)
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{
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for_each_sched_entity(se) {
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delta = calc_delta_mine(delta,
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cfs_rq_of(se)->load.weight, &se->load);
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}
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return delta;
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}
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/*
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* The idea is to set a period in which each task runs once.
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*
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@ -362,47 +390,54 @@ static u64 __sched_period(unsigned long nr_running)
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*/
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static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
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{
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u64 slice = __sched_period(cfs_rq->nr_running);
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for_each_sched_entity(se) {
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cfs_rq = cfs_rq_of(se);
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slice *= se->load.weight;
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do_div(slice, cfs_rq->load.weight);
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}
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return slice;
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return calc_delta_weight(__sched_period(cfs_rq->nr_running), se);
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}
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/*
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* We calculate the vruntime slice of a to be inserted task
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*
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* vs = s/w = p/rw
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* vs = s*rw/w = p
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*/
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static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
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{
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unsigned long nr_running = cfs_rq->nr_running;
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unsigned long weight;
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u64 vslice;
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if (!se->on_rq)
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nr_running++;
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vslice = __sched_period(nr_running);
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return __sched_period(nr_running);
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}
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/*
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* The goal of calc_delta_asym() is to be asymmetrically around NICE_0_LOAD, in
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* that it favours >=0 over <0.
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*
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* -20 |
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* |
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* 0 --------+-------
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* .'
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* 19 .'
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*
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*/
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static unsigned long
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calc_delta_asym(unsigned long delta, struct sched_entity *se)
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{
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struct load_weight lw = {
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.weight = NICE_0_LOAD,
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.inv_weight = 1UL << (WMULT_SHIFT-NICE_0_SHIFT)
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};
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for_each_sched_entity(se) {
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cfs_rq = cfs_rq_of(se);
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struct load_weight *se_lw = &se->load;
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weight = cfs_rq->load.weight;
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if (!se->on_rq)
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weight += se->load.weight;
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if (se->load.weight < NICE_0_LOAD)
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se_lw = &lw;
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vslice *= NICE_0_LOAD;
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do_div(vslice, weight);
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delta = calc_delta_mine(delta,
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cfs_rq_of(se)->load.weight, se_lw);
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}
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return vslice;
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return delta;
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}
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/*
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@ -419,11 +454,7 @@ __update_curr(struct cfs_rq *cfs_rq, struct sched_entity *curr,
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curr->sum_exec_runtime += delta_exec;
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schedstat_add(cfs_rq, exec_clock, delta_exec);
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delta_exec_weighted = delta_exec;
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if (unlikely(curr->load.weight != NICE_0_LOAD)) {
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delta_exec_weighted = calc_delta_fair(delta_exec_weighted,
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&curr->load);
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}
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delta_exec_weighted = calc_delta_fair(delta_exec, curr);
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curr->vruntime += delta_exec_weighted;
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}
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@ -632,8 +663,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
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/* sleeps upto a single latency don't count. */
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if (sched_feat(NEW_FAIR_SLEEPERS)) {
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if (sched_feat(NORMALIZED_SLEEPER))
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vruntime -= calc_delta_fair(sysctl_sched_latency,
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&cfs_rq->load);
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vruntime -= calc_delta_weight(sysctl_sched_latency, se);
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else
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vruntime -= sysctl_sched_latency;
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}
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@ -1132,11 +1162,10 @@ static unsigned long wakeup_gran(struct sched_entity *se)
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unsigned long gran = sysctl_sched_wakeup_granularity;
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/*
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* More easily preempt - nice tasks, while not making
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* it harder for + nice tasks.
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* More easily preempt - nice tasks, while not making it harder for
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* + nice tasks.
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*/
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if (unlikely(se->load.weight > NICE_0_LOAD))
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gran = calc_delta_fair(gran, &se->load);
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gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
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return gran;
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}
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