Hello Thomas, On Thu, Dec 18, 2014 at 11:51:01AM +0100, Thomas Gleixner wrote: > commit 4dbd27711cd9 "tick: export nohz tick idle symbols for module > use" was merged via the thermal tree without an explicit ack from the > relevant maintainers. >
This is a shame. Rui, do you have any comments on this?
> The exports are abused by the intel powerclamp driver which implements
> a fake idle state from a sched FIFO task. This causes all kinds of
> wreckage in the NOHZ core code which rightfully assumes that
> tick_nohz_idle_enter/exit() are only called from the idle task itself.
>
OK.
> Recent changes in the NOHZ core lead to a failure of the powerclamp
> driver and now people try to hack completely broken and backwards
> workarounds into the NOHZ core code. This is completely unacceptable.
>
I see.
> The real solution is to fix the powerclamp driver by rewriting it with
> a sane concept, but that's beyond the scope of this.
>
Do you have suggestions on what exactly is the expected rewriting or the
correct sane concepts?
> So the only solution for now is to remove the calls into the core NOHZ
> code from the powerclamp trainwreck along with the exports.
>
> Fixes: d6d71ee4a14a "PM: Introduce Intel PowerClamp Driver"
If I got it right, the driver is currently broken due to changes in NOHZ
core. So, does this patch fix power clamp behavior ?
If I got your proposal right, in the end power clamp will be still
broken, but at least won't be abusing NOHZ. Is that what you are
proposing?
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
> ---
> diff --git a/drivers/thermal/intel_powerclamp.c
> b/drivers/thermal/intel_powerclamp.c
> index b46c706e1cac..e98b4249187c 100644
> --- a/drivers/thermal/intel_powerclamp.c
> +++ b/drivers/thermal/intel_powerclamp.c
> @@ -435,7 +435,6 @@ static int clamp_thread(void *arg)
> * allowed. thus jiffies are updated properly.
> */
> preempt_disable();
> - tick_nohz_idle_enter();
> /* mwait until target jiffies is reached */
> while (time_before(jiffies, target_jiffies)) {
> unsigned long ecx = 1;
> @@ -451,7 +450,6 @@ static int clamp_thread(void *arg)
> start_critical_timings();
> atomic_inc(&idle_wakeup_counter);
> }
> - tick_nohz_idle_exit();
> preempt_enable();
> }
> del_timer_sync(&wakeup_timer);
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 4d54b7540585..1363d58f07e9 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -847,7 +847,6 @@ void tick_nohz_idle_enter(void)
>
> local_irq_enable();
> }
> -EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
>
> /**
> * tick_nohz_irq_exit - update next tick event from interrupt exit
> @@ -974,7 +973,6 @@ void tick_nohz_idle_exit(void)
>
> local_irq_enable();
> }
> -EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
>
> static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
> {
>
> --
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