I'm adding this to the next 3.12-rt release. -- Steve
>From 239f9f7716c6a2b466fcbb605fa0102de483c116 Mon Sep 17 00:00:00 2001 From: Mike Galbraith <[email protected]> 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 <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Steven Rostedt <[email protected]> --- 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 af7418b7d212..76873807655a 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 2cfd4c740042..3238cfbfbeeb 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -221,7 +221,12 @@ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
