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

From: Jacob Pan
Date: Mon Nov 16 2015 - 19:10:13 EST

On Mon, 16 Nov 2015 23:01:12 +0100 (CET)
Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> > For the second case, which is much more rare, I think we do have
> > next timer exactly one tick away. Just don't know why tick will
> > continue into idle loop.
> Well, it should not be hard to figure that out. There are not so many
> checks involved when tick_nohz_irq_exit() is called.
Thanks for the tip, I found the cause is in
int idle_cpu(int cpu)
if (rq->nr_running)
return 0;

Since we only take into account of cfs_rq runnable taking over
cfs_rq->nr_running when forced_idle is set.

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