On 15 April 2014 18:14, Frederic Weisbecker <fweis...@gmail.com> wrote:
> Sure but check out the static_key_false() in the implementation of
> tick_nohz_full_enabled().
> That's where the magic hides.
> No problem, the jump label/static key code is quite tricky. And its use
> can be easily missed, as in here.
>
> Also its unfamous API naming (static_key_true/static_key_true) that is
> anything but intuitive.
That was tricky enough to be missed on first look :)
Okay here is the answer to what you asked earlier:
>> In this case probably we can move !can_stop_full_tick() as well to the
>> wrapper ?
>
> Do you mean moving all the code of __tick_nohz_task_switch() to
> tick_nohz_task_switch()?
> I much prefer we don't do that. This is going to make can_stop_full_tick() a
> publicly
> visible nohz internal. And it may uglify tick.h as well.
I probably asked the wrong question, I meant tick_nohz_tick_stopped()
instead of !can_stop_full_tick().
Or, can we make the code more efficient by avoiding a branch by doing this:
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 1065a51..12632cc 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -220,7 +220,7 @@ static inline void tick_nohz_full_check(void)
static inline void tick_nohz_task_switch(void)
{
- if (tick_nohz_full_enabled())
+ if (tick_nohz_full_enabled() && tick_nohz_tick_stopped())
__tick_nohz_task_switch();
}
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 45037c4..904e09b 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -273,7 +273,7 @@ void __tick_nohz_task_switch(void)
local_irq_save(flags);
- if (tick_nohz_tick_stopped() && !can_stop_full_tick())
+ if (!can_stop_full_tick())
tick_nohz_full_kick();
local_irq_restore(flags);
--
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