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authorNicolas Pitre <nicolas.pitre@linaro.org>2014-12-03 14:43:06 -0500
committerJohn Stultz <john.stultz@linaro.org>2015-01-23 17:21:31 -0800
commit8b618628b2bf83512fc8df5e8672619d65adfdfb (patch)
treec295bed4f4e702f5f39fcce622258e55242b1d93
parenteaa27f34e91a14cdceed26ed6c6793ec1d186115 (diff)
downloadop-kernel-dev-8b618628b2bf83512fc8df5e8672619d65adfdfb.zip
op-kernel-dev-8b618628b2bf83512fc8df5e8672619d65adfdfb.tar.gz
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.h12
-rw-r--r--kernel/time/hrtimer.c4
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 */
/*
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