Messages in this thread Patch in this message | | | Date | Wed, 27 Dec 2017 19:22:06 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 2/4] nohz: Prevent erroneous tick stop invocations |
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On Tue, 26 Dec 2017, Frederic Weisbecker wrote:
> On Fri, Dec 22, 2017 at 03:51:13PM +0100, Thomas Gleixner wrote: > > The conditions in irq_exit() to invoke tick_nohz_irq_exit() are: > > > > if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) > > > > This is too permissive in various aspects: > > > > 1) If need_resched() is set, then the tick cannot be stopped whether > > the CPU is idle or in nohz full mode. > > That's not exactly true. In nohz full mode the tick is not restarted on the > switch from idle to a single task. And if an idle interrupt wakes up a > single task and enqueues a timer, we want that timer to be programmed even > though we have need_resched().
Hrmm, so the check for softirq_pending() should be sufficient, right?
--- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -382,7 +382,8 @@ static inline void tick_irq_exit(void) int cpu = smp_processor_id(); /* Make sure that timer wheel updates are propagated */ - if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) { + if (((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) && + if ((idle_cpu(cpu) || tick_nohz_full_cpu(cpu)) && + !local_softirq_pending()) { if (!in_interrupt()) tick_nohz_irq_exit(); }
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