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clocksource: Move cycle_last validation to core code

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The only user of the cycle_last validation is the x86 TSC. In order to
provide NMI safe accessor functions for clock monotonic and
monotonic_raw we need to do that in the core.

We can't do the TSC specific

    if (now < cycle_last)
       	    now = cycle_last;

for the other wrapping around clocksources, but TSC has
CLOCKSOURCE_MASK(64) which actually does not mask out anything so if
now is less than cycle_last the subtraction will give a negative
result. So we can check for that in clocksource_delta() and return 0
for that case.

Implement and enable it for x86

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Thomas Gleixner
2014-07-16 21:05:12 +00:00
committed by John Stultz
parent 3a97837784
commit 09ec54429c
4 changed files with 24 additions and 12 deletions
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9
kernel/time/timekeeping_internal.h
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@@ -12,9 +12,18 @@ extern void tk_debug_account_sleep_time(struct timespec64 *t);
#define tk_debug_account_sleep_time(x)
#endif
#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
{
cycle_t ret = (now - last) & mask;
return (s64) ret > 0 ? ret : 0;
}
#else
static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
{
return (now - last) & mask;
}
#endif
#endif /* _TIMEKEEPING_INTERNAL_H */