On Fri, 2015-04-10 at 16:15 +0200, Sebastian Andrzej Siewior wrote: > * Mike Galbraith | 2015-03-13 05:53:25 [+0100]: > > > First of all, a task being ticked and trying to shut the tick down > > will > > fail to do so due to having just awakened ksoftirqd, so let > > ksoftirqd > > try to do that after SOFTIRQ_TIMER processing. Secondly, should > > the > > tick be shut down, we may livelock in hrtimer-cancel() because in - > > rt > > a callback may be running. Break the loop, and let > > tick_nohz_restart() > > know that the timer is busy so it can bail. > > So with this patch > http://marc.info/?l=linux-rt-users&m=142866940327602&w=2 @@ -117,10 +113,8 @@ bool irq_work_queue(struct irq_work *wor if (work->flags & IRQ_WORK_HARD_IRQ) { if (llist_add(&work->llnode, this_cpu_ptr(&hirq_work_list))) arch_irq_work_raise(); - } else { - if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list))) - arch_irq_work_raise(); - } + } /* for lazy_list we have the timer irq */ If we don't queue work without IRQ_WORK_HARD_IRQ set, how does it run? Anyway, box did not livelock, nor did it with that bit reverted. > you could drop the hrtimer hacks. Is this the remaining part all > that is > required or we shorten the following patch a little more? 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> --- kernel/sched/core.c | 17 ++++++++++++++++- kernel/time/tick-sched.c | 5 +++++ 2 files changed, 21 insertions(+), 1 deletion(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -781,14 +781,29 @@ static inline bool got_nohz_idle_kick(vo #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) { /* * More than one running task need preemption. * nr_running update is assumed to be visible * after IPI is sent from wakers. + * + * NOTE, RT: if ksoftirqd is awake, subtract it. */ - if (this_rq()->nr_running > 1) + if (this_rq()->nr_running - ksoftirqd_running() > 1) return false; return true; --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -227,7 +227,12 @@ 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) = { -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
