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clocksource: Extract max nsec calculation into separate function

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We need to calculate the same number in the clocksource code and
the sched_clock code, so extract this code into its own function.
We also drop the min_t and just use min() because the two types
are the same.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Stephen Boyd 2013-07-18 16:21:14 -07:00 committed by John Stultz
parent ad81f0545e
commit 87d8b9eb7e
2 changed files with 32 additions and 15 deletions
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2
include/linux/clocksource.h
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@ -292,6 +292,8 @@ extern void clocksource_resume(void);
extern struct clocksource * __init __weak clocksource_default_clock(void);
extern void clocksource_mark_unstable(struct clocksource *cs);
extern u64
clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask);
extern void
clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec);

45
kernel/time/clocksource.c
View file

@ -537,40 +537,55 @@ static u32 clocksource_max_adjustment(struct clocksource *cs)
}
/**
* clocksource_max_deferment - Returns max time the clocksource can be deferred
* @cs: Pointer to clocksource
*
* clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
* @mult: cycle to nanosecond multiplier
* @shift: cycle to nanosecond divisor (power of two)
* @maxadj: maximum adjustment value to mult (~11%)
* @mask: bitmask for two's complement subtraction of non 64 bit counters
*/
static u64 clocksource_max_deferment(struct clocksource *cs)
u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
{
u64 max_nsecs, max_cycles;
/*
* Calculate the maximum number of cycles that we can pass to the
* cyc2ns function without overflowing a 64-bit signed result. The
* maximum number of cycles is equal to ULLONG_MAX/(cs->mult+cs->maxadj)
* maximum number of cycles is equal to ULLONG_MAX/(mult+maxadj)
* which is equivalent to the below.
* max_cycles < (2^63)/(cs->mult + cs->maxadj)
* max_cycles < 2^(log2((2^63)/(cs->mult + cs->maxadj)))
* max_cycles < 2^(log2(2^63) - log2(cs->mult + cs->maxadj))
* max_cycles < 2^(63 - log2(cs->mult + cs->maxadj))
* max_cycles < 1 << (63 - log2(cs->mult + cs->maxadj))
* max_cycles < (2^63)/(mult + maxadj)
* max_cycles < 2^(log2((2^63)/(mult + maxadj)))
* max_cycles < 2^(log2(2^63) - log2(mult + maxadj))
* max_cycles < 2^(63 - log2(mult + maxadj))
* max_cycles < 1 << (63 - log2(mult + maxadj))
* Please note that we add 1 to the result of the log2 to account for
* any rounding errors, ensure the above inequality is satisfied and
* no overflow will occur.
*/
max_cycles = 1ULL << (63 - (ilog2(cs->mult + cs->maxadj) + 1));
max_cycles = 1ULL << (63 - (ilog2(mult + maxadj) + 1));
/*
* The actual maximum number of cycles we can defer the clocksource is
* determined by the minimum of max_cycles and cs->mask.
* determined by the minimum of max_cycles and mask.
* Note: Here we subtract the maxadj to make sure we don't sleep for
* too long if there's a large negative adjustment.
*/
max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult - cs->maxadj,
cs->shift);
max_cycles = min(max_cycles, mask);
max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
return max_nsecs;
}
/**
* clocksource_max_deferment - Returns max time the clocksource can be deferred
* @cs: Pointer to clocksource
*
*/
static u64 clocksource_max_deferment(struct clocksource *cs)
{
u64 max_nsecs;
max_nsecs = clocks_calc_max_nsecs(cs->mult, cs->shift, cs->maxadj,
cs->mask);
/*
* To ensure that the clocksource does not wrap whilst we are idle,
* limit the time the clocksource can be deferred by 12.5%. Please