I'm adding this patch to the next 3.14-rt release.
-- Steve
>From b59089f83e5bea79c86bf0726c98529c2afb09cc Mon Sep 17 00:00:00 2001
From: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Date: Sat, 11 Apr 2015 15:15:59 +0200
Subject: [PATCH] rt, nohz_full: fix nohz_full for PREEMPT_RT_FULL
A task being ticked and trying to shut the tick down will fail due
to having just awakened ksoftirqd, subtract it from nr_running.
Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
kernel/sched/core.c | 29 +++++++++++++++++++++++------
kernel/time/tick-sched.c | 5 +++++
2 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 883669d3e293..71c0bb1cdeb0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -696,17 +696,34 @@ static inline bool got_nohz_idle_kick(void)
#endif /* CONFIG_NO_HZ_COMMON */
#ifdef CONFIG_NO_HZ_FULL
+
+static int ksoftirqd_running(void)
+{
+ struct task_struct *softirqd;
+
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT_FULL))
+ return 0;
+ softirqd = this_cpu_ksoftirqd();
+ if (softirqd && softirqd->on_rq)
+ return 1;
+ return 0;
+}
+
bool sched_can_stop_tick(void)
{
- struct rq *rq;
+ struct rq *rq;
- rq = this_rq();
+ rq = this_rq();
- /* Make sure rq->nr_running update is visible after the IPI */
- smp_rmb();
+ /* Make sure rq->nr_running update is visible after the IPI */
+ smp_rmb();
- /* More than one running task need preemption */
- if (rq->nr_running > 1)
+ /*
+ * More than one running task need preemption
+ *
+ * NOTE, RT: if ksoftirqd is awake, subtract it.
+ */
+ if (rq->nr_running - ksoftirqd_running() > 1)
return false;
return true;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6c97081f67f9..57d5bb1b3919 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -226,7 +226,12 @@ void __tick_nohz_full_check(void)
static void nohz_full_kick_work_func(struct irq_work *work)
{
+ unsigned long flags;
+
+ /* ksoftirqd processes sirqs with interrupts enabled */
+ local_irq_save(flags);
__tick_nohz_full_check();
+ local_irq_restore(flags);
}
static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
--
2.1.4
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