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powerpc/time: Sanity check of decrementer expiration is necessary

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commit 860aed25a1 upstream.

This reverts 68568add2c ("powerpc/time: Remove unnecessary sanity check
of decrementer expiration").  We do need to check whether we have reached
the expiration time of the next event, because we sometimes get an early
decrementer interrupt, most notably when we set the decrementer to 1 in
arch_irq_work_raise().  The effect of not having the sanity check is that
if timer_interrupt() gets called early, we leave the decrementer set to
its maximum value, which means we then don't get any more decrementer
interrupts for about 4 seconds (or longer, depending on timebase
frequency).  I saw these pauses as a consequence of getting a stray
hypervisor decrementer interrupt left over from exiting a KVM guest.

This isn't quite a straight revert because of changes to the surrounding
code, but it restores the same algorithm as was previously used.

Acked-by: Anton Blanchard <anton@samba.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Paul Mackerras 2012-06-01 18:13:43 +10:00 committed by Greg Kroah-Hartman
parent 5a32293d5c
commit e6a6c7d2e5
1 changed files with 11 additions and 3 deletions
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14
arch/powerpc/kernel/time.c
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@ -474,6 +474,7 @@ void timer_interrupt(struct pt_regs * regs)
struct pt_regs *old_regs;
u64 *next_tb = &__get_cpu_var(decrementers_next_tb);
struct clock_event_device *evt = &__get_cpu_var(decrementers);
u64 now;
/* Ensure a positive value is written to the decrementer, or else
* some CPUs will continue to take decrementer exceptions.
@ -508,9 +509,16 @@ void timer_interrupt(struct pt_regs * regs)
irq_work_run();
}
*next_tb = ~(u64)0;
if (evt->event_handler)
evt->event_handler(evt);
now = get_tb_or_rtc();
if (now >= *next_tb) {
*next_tb = ~(u64)0;
if (evt->event_handler)
evt->event_handler(evt);
} else {
now = *next_tb - now;
if (now <= DECREMENTER_MAX)
set_dec((int)now);
}
#ifdef CONFIG_PPC64
/* collect purr register values often, for accurate calculations */