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powerpc/time: improve decrementer clockevent processing 

The stop/shutdown op should not use decrementer_set_next_event because
that sets decrementers_next_tb to now + decrementer_max, which means a
decrementer interrupt that occurs after that time will call the
clockevent event handler unexpectedly. Set next_tb to ~0 here to prevent
any clock event call. Init all clockevents to stopped.

Then the decrementer clockevent device always has event_handler set and
applicable because we know the clock event device was not stopped. So
make this call unconditional to show that it is always called. next_tb
need not be set to ~0 before the event handler is called because it will
stop the clockevent device if there is no other timer.

Finally, the timer broadcast interrupt should not modify next_tb because
it is not involved with the local decrementer clockevent on this CPU.

This doesn't fix a known bug, just tidies the code.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220124143930.3923442-3-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-01-25 00:39:30 +10:00 committed by Michael Ellerman
parent cf74ff52e3
commit 35de589cb8
1 changed files with 10 additions and 8 deletions
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18
arch/powerpc/kernel/time.c
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@ -107,7 +107,12 @@ struct clock_event_device decrementer_clockevent = {
};
EXPORT_SYMBOL(decrementer_clockevent);
DEFINE_PER_CPU(u64, decrementers_next_tb);
/*
* This always puts next_tb beyond now, so the clock event will never fire
* with the usual comparison, no need for a separate test for stopped.
*/
#define DEC_CLOCKEVENT_STOPPED ~0ULL
DEFINE_PER_CPU(u64, decrementers_next_tb) = DEC_CLOCKEVENT_STOPPED;
EXPORT_SYMBOL_GPL(decrementers_next_tb);
static DEFINE_PER_CPU(struct clock_event_device, decrementers);
@ -645,9 +650,7 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
now = get_tb();
if (now >= *next_tb) {
*next_tb = ~(u64)0;
if (evt->event_handler)
evt->event_handler(evt);
evt->event_handler(evt);
__this_cpu_inc(irq_stat.timer_irqs_event);
} else {
now = *next_tb - now;
@ -666,9 +669,6 @@ EXPORT_SYMBOL(timer_interrupt);
#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
void timer_broadcast_interrupt(void)
{
u64 *next_tb = this_cpu_ptr(&decrementers_next_tb);
*next_tb = ~(u64)0;
tick_receive_broadcast();
__this_cpu_inc(irq_stat.broadcast_irqs_event);
}
@ -894,7 +894,9 @@ static int decrementer_set_next_event(unsigned long evt,
static int decrementer_shutdown(struct clock_event_device *dev)
{
decrementer_set_next_event(decrementer_max, dev);
__this_cpu_write(decrementers_next_tb, DEC_CLOCKEVENT_STOPPED);
set_dec_or_work(decrementer_max);
return 0;
}