On 15 April 2014 18:14, Frederic Weisbecker fweisbec@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);