xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

ktime: Optimize ktime_divns for constant divisors

Browse Source 
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>
This commit is contained in:
Nicolas Pitre
2014-12-03 14:43:06 -05:00
committed by John Stultz
parent eaa27f34e9
commit 8b618628b2
2 changed files with 13 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/ktime.h
View File

@@ -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