On Tue, Dec 17, 2013 at 11:51:30PM +0100, Frederic Weisbecker wrote:
> When a full dynticks CPU wakes up from sysidle state, which means that
> all full dynticks CPUs were previously sleeping, it's possible that
> all the potential timekeeping CPUs are sleeping as well and nobody
> maintains the associated duty.
>
> But full dynticks CPUs don't run the tick by definition so we need
> to wake up a timekeeper such that it can handle the timekeeping
> duty on behalf of the freshly awoken full dyntick CPU.
>
> To achieve this and ensure that this CPU won't deal with stale
> jiffies values, lets wake up the default timekeeper using the right
> API.
>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: John Stultz <john.stu...@linaro.org>
> Cc: Alex Shi <alex....@linaro.org>
> Cc: Kevin Hilman <khil...@linaro.org>
> ---
> kernel/rcu/tree_plugin.h | 2 +-
> kernel/time/tick-sched.c | 3 ++-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 1795265..b43e32d 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2488,7 +2488,7 @@ void rcu_sysidle_force_exit(void)
> oldstate, RCU_SYSIDLE_NOT);
> if (oldstate == newoldstate &&
> oldstate == RCU_SYSIDLE_FULL_NOTED) {
> - smp_send_reschedule(tick_timekeeping_default_cpu());
> + tick_nohz_full_kick_timekeeping();
OK, I guess I should look at the patches in order. So yes, it is no
longer safe to just kick tick_do_timer_cpu. ;-)
Never mind my question on patch 12/13 in this series.
Thanx, Paul
> return; /* We cleared it, done! */
> }
> oldstate = newoldstate;
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 94b6901..f5ae69f 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -302,7 +302,8 @@ void tick_nohz_full_kick_all(void)
> /**
> * tick_nohz_full_kick_timekeeping - kick the default timekeeper
> *
> - * kick the default timekeeper when a secondary timekeeper goes offline.
> + * kick the default timekeeper when full dynticks CPUs exit full
> + * system idle state or when a secondary timekeeper goes offline.
> */
> void tick_nohz_full_kick_timekeeping(void)
> {
> --
> 1.8.3.1
>
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