[PATCH] timer: nohz: don't disable the timer if we don't have irqwork interrupt

[PATCH] timer: nohz: don't disable the timer if we don't have irqwork interrupt

[Sebastian Andrzej Siewior]

The irq work interrupt is optional: If an architecture does not provide
it then the callback will be run from update_process_times(). This does
not work well for nohz_full_kick_work_func() as we learned in commit
76a33061b932 ("irq_work: Force raised irq work to run on irq work
interrupt").

This patch is just a precaution to ensure that that an irq work
interrupt is required and the timer callback is not enough.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/time/tick-sched.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c792429e98c6..d9481bebae22 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -176,6 +176,11 @@ static bool can_stop_full_tick(void)
 		return false;
 	}
 
+	if (!arch_irq_work_has_interrupt()) {
+		trace_tick_stop(0, "missing irq work interrupt\n");
+		return false;
+	}
+
 	/* sched_clock_tick() needs us? */
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 	/*
-- 
2.1.4

Re: [PATCH] timer: nohz: don't disable the timer if we don't have irqwork interrupt

[Frederic Weisbecker]

On Tue, Jun 23, 2015 at 04:07:43PM +0200, Sebastian Andrzej Siewior wrote:
> The irq work interrupt is optional: If an architecture does not provide
> it then the callback will be run from update_process_times(). This does
> not work well for nohz_full_kick_work_func() as we learned in commit
> 76a33061b932 ("irq_work: Force raised irq work to run on irq work
> interrupt").
> 
> This patch is just a precaution to ensure that that an irq work
> interrupt is required and the timer callback is not enough.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

But we already check that in tick_nohz_init(). Or am I missing something
else?

Thanks.

> ---
>  kernel/time/tick-sched.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index c792429e98c6..d9481bebae22 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -176,6 +176,11 @@ static bool can_stop_full_tick(void)
>  		return false;
>  	}
>  
> +	if (!arch_irq_work_has_interrupt()) {
> +		trace_tick_stop(0, "missing irq work interrupt\n");
> +		return false;
> +	}
> +
>  	/* sched_clock_tick() needs us? */
>  #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
>  	/*
> -- 
> 2.1.4
> 

Re: [PATCH] timer: nohz: don't disable the timer if we don't have irqwork interrupt

[Sebastian Andrzej Siewior]

On 07/07/2015 04:16 PM, Frederic Weisbecker wrote:
> But we already check that in tick_nohz_init(). Or am I missing something
> else?

Ah indeed, thanks. Haven't seen it.

> 
> Thanks.

Sebastian