diff options
| author | Nicolas Pitre <nicolas.pitre@linaro.org> | 2014-12-03 14:43:06 -0500 |
|---|---|---|
| committer | John Stultz <john.stultz@linaro.org> | 2015-01-23 17:21:31 -0800 |
| commit | 8b618628b2bf83512fc8df5e8672619d65adfdfb (patch) | |
| tree | c295bed4f4e702f5f39fcce622258e55242b1d93 | |
| parent | eaa27f34e91a14cdceed26ed6c6793ec1d186115 (diff) | |
| download | lwn-8b618628b2bf83512fc8df5e8672619d65adfdfb.tar.gz lwn-8b618628b2bf83512fc8df5e8672619d65adfdfb.zip | |
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 <arnd.bergmann@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Nicolas Pitre <nico@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
| -rw-r--r-- | include/linux/ktime.h | 12 | ||||
| -rw-r--r-- | 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 c9d645ad98ff..411dd8bfe539 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 37e50aadd471..890535c41c2d 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 */ /* |