ktime: Optimize ktime_divns for constant divisors (8b618628) · Commits · 戴 / test

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>

include/linux/ktime.h

+11 −1

Original line number	Diff line number	Diff line
		@@ -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

kernel/time/hrtimer.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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 */

		/*

Admin message