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Date: Wed, 17 Jun 2015 15:23:20 -0700 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Arnd Bergmann <arnd.bergmann@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Nicolas Pitre <nico@...aro.org>, John Stultz <john.stultz@...aro.org>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 3.19.y-ckt 095/146] ktime: Optimize ktime_divns for constant divisors 3.19.8-ckt2 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Nicolas Pitre <nicolas.pitre@...aro.org> commit 8b618628b2bf83512fc8df5e8672619d65adfdfb upstream. 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@...aro.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Ingo Molnar <mingo@...nel.org> Cc: Nicolas Pitre <nico@...aro.org> Acked-by: Arnd Bergmann <arnd@...db.de> Signed-off-by: Nicolas Pitre <nico@...aro.org> Signed-off-by: John Stultz <john.stultz@...aro.org> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- 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 d8c724c..5e4d51c 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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