Commit 8b618628 authored by Nicolas Pitre's avatar Nicolas Pitre Committed by John Stultz

ktime: Optimize ktime_divns for constant divisors

At least on ARM, do_div() is optimized to turn constant divisors into
an inline multiplication by the reciprocal value at compile time.
However this optimization is missed entirely whenever ktime_divns() is
used and the slow out-of-line division code is used all the time.

Let ktime_divns() use do_div() inline whenever the divisor is constant
and small enough.  This will make things like ktime_to_us() and
ktime_to_ms() much faster.

Cc: Arnd Bergmann <>
Cc: Thomas Gleixner <>
Cc: Ingo Molnar <>
Cc: Nicolas Pitre <>
Acked-by: default avatarArnd Bergmann <>
Signed-off-by: default avatarNicolas Pitre <>
Signed-off-by: default avatarJohn Stultz <>
parent eaa27f34
......@@ -166,7 +166,17 @@ static inline bool ktime_before(const ktime_t cmp1, const ktime_t cmp2)
#if BITS_PER_LONG < 64
extern u64 ktime_divns(const ktime_t kt, s64 div);
extern u64 __ktime_divns(const ktime_t kt, s64 div);
static inline u64 ktime_divns(const ktime_t kt, s64 div)
if (__builtin_constant_p(div) && !(div >> 32)) {
u64 ns = kt.tv64;
do_div(ns, div);
return ns;
} else {
return __ktime_divns(kt, div);
#else /* BITS_PER_LONG < 64 */
# define ktime_divns(kt, div) (u64)((kt).tv64 / (div))
......@@ -266,7 +266,7 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
* Divide a ktime value by a nanosecond value
u64 ktime_divns(const ktime_t kt, s64 div)
u64 __ktime_divns(const ktime_t kt, s64 div)
u64 dclc;
int sft = 0;
......@@ -282,7 +282,7 @@ u64 ktime_divns(const ktime_t kt, s64 div)
return dclc;
#endif /* BITS_PER_LONG >= 64 */
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