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sched: prevent wakeup over-scheduling

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Prevent wakeup over-scheduling.  Once a task has been preempted by a
task of the same or lower priority, it becomes ineligible for repeated
preemption by same until it has been ticked, or slept.  Instead, the
task is marked for preemption at the next tick.  Tasks of higher
priority still preempt immediately.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mike Galbraith 2007-10-15 17:00:14 +02:00 committed by Ingo Molnar
parent ce6c131131
commit 95938a35c5
3 changed files with 15 additions and 4 deletions
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1
include/linux/sched.h
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@ -912,6 +912,7 @@ struct sched_entity {
struct load_weight load; /* for load-balancing */
struct rb_node run_node;
unsigned int on_rq;
int peer_preempt;
u64 exec_start;
u64 sum_exec_runtime;

4
kernel/sched.c
View File

@ -445,6 +445,7 @@ enum {
SCHED_FEAT_TREE_AVG = 4,
SCHED_FEAT_APPROX_AVG = 8,
SCHED_FEAT_WAKEUP_PREEMPT = 16,
SCHED_FEAT_PREEMPT_RESTRICT = 32,
};
const_debug unsigned int sysctl_sched_features =
@ -452,7 +453,8 @@ const_debug unsigned int sysctl_sched_features =
SCHED_FEAT_START_DEBIT *1 |
SCHED_FEAT_TREE_AVG *0 |
SCHED_FEAT_APPROX_AVG *0 |
SCHED_FEAT_WAKEUP_PREEMPT *1;
SCHED_FEAT_WAKEUP_PREEMPT *1 |
SCHED_FEAT_PREEMPT_RESTRICT *1;
#define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x)

14
kernel/sched_fair.c
View File

@ -526,6 +526,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
update_stats_dequeue(cfs_rq, se);
if (sleep) {
se->peer_preempt = 0;
#ifdef CONFIG_SCHEDSTATS
if (entity_is_task(se)) {
struct task_struct *tsk = task_of(se);
@ -553,8 +554,10 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
ideal_runtime = sched_slice(cfs_rq, curr);
delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
if (delta_exec > ideal_runtime)
if (delta_exec > ideal_runtime ||
(sched_feat(PREEMPT_RESTRICT) && curr->peer_preempt))
resched_task(rq_of(cfs_rq)->curr);
curr->peer_preempt = 0;
}
static void
@ -839,8 +842,12 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
if (unlikely(se->load.weight != NICE_0_LOAD))
gran = calc_delta_fair(gran, &se->load);
if (delta > gran)
resched_task(curr);
if (delta > gran) {
int now = !sched_feat(PREEMPT_RESTRICT);
if (now || p->prio < curr->prio || !se->peer_preempt++)
resched_task(curr);
}
}
}
@ -1034,6 +1041,7 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
check_spread(cfs_rq, curr);
__enqueue_entity(cfs_rq, se);
account_entity_enqueue(cfs_rq, se);
se->peer_preempt = 0;
resched_task(rq->curr);
}