From: Nicolas Pitre <nicolas.pi...@linaro.org>
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 <arnd.bergm...@linaro.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Nicolas Pitre <n...@linaro.org>
Acked-by: Arnd Bergmann <a...@arndb.de>
Signed-off-by: Nicolas Pitre <n...@linaro.org>
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
include/linux/ktime.h | 12 +++++++++++-
kernel/time/hrtimer.c | 4 ++--
2 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index c9d645a..411dd8b 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -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))
#endif
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 37e50aa..890535c 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -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;
}
-EXPORT_SYMBOL_GPL(ktime_divns);
+EXPORT_SYMBOL_GPL(__ktime_divns);
#endif /* BITS_PER_LONG >= 64 */
/*
--
1.9.1
--
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