Re: [PATCH 2/4] timer: relax tick stop in idle entry

Peter Zijlstra
2015-11-19T19:59:13Z

On Thu, Nov 19, 2015 at 11:21:25AM -0800, Jacob Pan wrote:
> On Thu, 19 Nov 2015 20:06:30 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > Which one? That is, I cannot find a idle_cpu() call from
> > tick_nohz_irq_exit().
> it is tick_irq_exit(void), i will not call tick_nohz_irq_exit() if
> !idle_cpu()

Ah, but I think we really only need to test for the idle task there, the
&& need_resched() part of that function takes care of the rest.

Once we have need_resched() set, we'll be on our way to
tick_nohz_idle_exit() to restart the tick again.

---
kernel/softirq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 479e4436f787..3bd30404f2ee 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -367,7 +367,7 @@ 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 ((is_idle_task(current) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
if (!in_interrupt())
tick_nohz_irq_exit();
}