sched: re-instate vruntime based wakeup preemption
The advantage is that vruntime based wakeup preemption has a better conceptual model. Here wakeup_gran = 0 means: preempt when 'fair'. Therefore wakeup_gran is the granularity of unfairness we allow in order to make progress. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -143,6 +143,49 @@ static inline struct sched_entity *parent_entity(struct sched_entity *se)
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return se->parent;
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}
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/* return depth at which a sched entity is present in the hierarchy */
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static inline int depth_se(struct sched_entity *se)
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{
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int depth = 0;
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for_each_sched_entity(se)
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depth++;
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return depth;
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}
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static void
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find_matching_se(struct sched_entity **se, struct sched_entity **pse)
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{
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int se_depth, pse_depth;
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/*
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* preemption test can be made between sibling entities who are in the
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* same cfs_rq i.e who have a common parent. Walk up the hierarchy of
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* both tasks until we find their ancestors who are siblings of common
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* parent.
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*/
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/* First walk up until both entities are at same depth */
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se_depth = depth_se(*se);
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pse_depth = depth_se(*pse);
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while (se_depth > pse_depth) {
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se_depth--;
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*se = parent_entity(*se);
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}
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while (pse_depth > se_depth) {
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pse_depth--;
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*pse = parent_entity(*pse);
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}
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while (!is_same_group(*se, *pse)) {
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*se = parent_entity(*se);
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*pse = parent_entity(*pse);
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}
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}
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#else /* CONFIG_FAIR_GROUP_SCHED */
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static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
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@ -193,6 +236,11 @@ static inline struct sched_entity *parent_entity(struct sched_entity *se)
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return NULL;
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}
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static inline void
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find_matching_se(struct sched_entity **se, struct sched_entity **pse)
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{
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}
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#endif /* CONFIG_FAIR_GROUP_SCHED */
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@ -1244,12 +1292,41 @@ static unsigned long wakeup_gran(struct sched_entity *se)
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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 (sched_feat(ASYM_GRAN))
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gran = calc_delta_mine(gran, NICE_0_LOAD, &se->load);
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if (!sched_feat(ASYM_GRAN) || se->load.weight > NICE_0_LOAD)
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gran = calc_delta_fair(sysctl_sched_wakeup_granularity, se);
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return gran;
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}
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/*
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* Should 'se' preempt 'curr'.
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*
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* |s1
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* |s2
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* |s3
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* g
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* |<--->|c
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*
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* w(c, s1) = -1
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* w(c, s2) = 0
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* w(c, s3) = 1
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*
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*/
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static int
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wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
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{
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s64 gran, vdiff = curr->vruntime - se->vruntime;
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if (vdiff <= 0)
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return -1;
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gran = wakeup_gran(curr);
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if (vdiff > gran)
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return 1;
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return 0;
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}
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/*
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* Preempt the current task with a newly woken task if needed:
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*/
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@ -1258,7 +1335,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
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struct task_struct *curr = rq->curr;
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struct cfs_rq *cfs_rq = task_cfs_rq(curr);
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struct sched_entity *se = &curr->se, *pse = &p->se;
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s64 delta_exec;
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if (unlikely(rt_prio(p->prio))) {
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update_rq_clock(rq);
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@ -1296,9 +1372,19 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
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return;
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}
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delta_exec = se->sum_exec_runtime - se->prev_sum_exec_runtime;
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if (delta_exec > wakeup_gran(pse))
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find_matching_se(&se, &pse);
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while (se) {
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BUG_ON(!pse);
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if (wakeup_preempt_entity(se, pse) == 1) {
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resched_task(curr);
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break;
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}
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se = parent_entity(se);
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pse = parent_entity(pse);
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}
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}
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static struct task_struct *pick_next_task_fair(struct rq *rq)
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