Hi Frederic,
The tick wakes ksoftirqd, ensuring nr_running test ain't gonna happen
when an otherwise lonely task takes the timer interrupt. Deferring to
softirq processing time..... works.
---
kernel/sched/core.c | 2 +-
kernel/softirq.c | 10 ++++++++++
kernel/time/tick-sched.c | 2 ++
3 files changed, 13 insertions(+), 1 deletion(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -704,7 +704,7 @@ bool sched_can_stop_tick(void)
smp_rmb();
/* More than one running task need preemption */
- if (rq->nr_running > 1)
+ if (rq->nr_running - (rq->curr == this_cpu_ksoftirqd()) > 1)
return false;
return true;
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -529,6 +529,11 @@ static void do_current_softirqs(int need
softirq_clr_runner(i);
unlock_softirq(i);
WARN_ON(current->softirq_nestcnt != 1);
+
+#ifdef CONFIG_NO_HZ_COMMON
+ if (i == TIMER_SOFTIRQ && tick_nohz_full_cpu(raw_smp_processor_id()))
+ tick_nohz_irq_exit();
+#endif
}
}
@@ -728,6 +733,11 @@ static inline void tick_irq_exit(void)
#ifdef CONFIG_NO_HZ_COMMON
int cpu = smp_processor_id();
+#ifdef CONFIG_PREEMPT_RT_FULL
+ if (tick_nohz_full_cpu(cpu))
+ return;
+#endif
+
/* Make sure that timer wheel updates are propagated */
if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
if (!in_interrupt())
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -157,7 +157,9 @@ bool have_nohz_full_mask;
static bool can_stop_full_tick(void)
{
+#ifndef CONFIG_PREEMPT_RT_FULL
WARN_ON_ONCE(!irqs_disabled());
+#endif
if (!sched_can_stop_tick()) {
trace_tick_stop(0, "more than 1 task in runqueue\n");
--
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