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sched: Add rq::ttwu_pending 

In preparation of removing rq->wake_list, replace the
!list_empty(rq->wake_list) with rq->ttwu_pending. This is not fully
equivalent as this new variable is racy.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200526161908.070399698@infradead.org
This commit is contained in:
Peter Zijlstra 2020-05-26 18:11:03 +02:00 committed by Ingo Molnar
parent 4b44a21dd6
commit 126c2092e5
4 changed files with 15 additions and 5 deletions
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13
kernel/sched/core.c
View File

@ -2275,13 +2275,21 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
void sched_ttwu_pending(void)
{
struct rq *rq = this_rq();
struct llist_node *llist = llist_del_all(&rq->wake_list);
struct llist_node *llist;
struct task_struct *p, *t;
struct rq_flags rf;
llist = llist_del_all(&rq->wake_list);
if (!llist)
return;
/*
* rq::ttwu_pending racy indication of out-standing wakeups.
* Races such that false-negatives are possible, since they
* are shorter lived that false-positives would be.
*/
WRITE_ONCE(rq->ttwu_pending, 0);
rq_lock_irqsave(rq, &rf);
update_rq_clock(rq);
@ -2318,6 +2326,7 @@ static void __ttwu_queue_wakelist(struct task_struct *p, int cpu, int wake_flags
p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
WRITE_ONCE(rq->ttwu_pending, 1);
if (llist_add(&p->wake_entry, &rq->wake_list)) {
if (!set_nr_if_polling(rq->idle))
smp_call_function_single_async(cpu, &rq->wake_csd);
@ -4705,7 +4714,7 @@ int idle_cpu(int cpu)
return 0;
#ifdef CONFIG_SMP
if (!llist_empty(&rq->wake_list))
if (rq->ttwu_pending)
return 0;
#endif

1
kernel/sched/debug.c
View File

@ -638,7 +638,6 @@ do { \
P(nr_running);
P(nr_switches);
P(nr_load_updates);
P(nr_uninterruptible);
PN(next_balance);
SEQ_printf(m, " .%-30s: %ld\n", "curr->pid", (long)(task_pid_nr(rq->curr)));

2
kernel/sched/fair.c
View File

@ -8590,7 +8590,7 @@ static int idle_cpu_without(int cpu, struct task_struct *p)
*/
#ifdef CONFIG_SMP
if (!llist_empty(&rq->wake_list))
if (rq->ttwu_pending)
return 0;
#endif

4
kernel/sched/sched.h
View File

@ -895,7 +895,9 @@ struct rq {
atomic_t nohz_flags;
#endif /* CONFIG_NO_HZ_COMMON */
unsigned long nr_load_updates;
#ifdef CONFIG_SMP
unsigned int ttwu_pending;
#endif
u64 nr_switches;
#ifdef CONFIG_UCLAMP_TASK