The following commit has been merged into the sched/core branch of tip:
Commit-ID: 126c2092e5c8b28623cb890cd2930aa292410676
Gitweb: https://git.kernel.org/tip/126c2092e5c8b28623cb890cd2930aa292410676
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 26 May 2020 18:11:03 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 28 May 2020 10:54:16 +02:00
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@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200526161908.070399698@xxxxxxxxxxxxx
---
kernel/sched/core.c | 13 +++++++++++--
kernel/sched/debug.c | 1 -
kernel/sched/fair.c | 2 +-
kernel/sched/sched.h | 4 +++-
4 files changed, 15 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fa0d499..b71ed5e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 1c24a6b..36c5426 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -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)));
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2890bd5..0ed04d2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 75b0629..c86fc94 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -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
|