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time: Optimize ns_to_timespec64()

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ns_to_timespec64() calls div_s64_rem(), which is a rather slow function on
32-bit architectures, as it cannot take advantage of the do_div()
optimizations for constant arguments.

Open-code the div_s64_rem() function in ns_to_timespec64(), so a constant
divider can be passed into the optimized div_u64_rem() function.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191108203435.112759-3-arnd@arndb.de
This commit is contained in:
Arnd Bergmann 2019-11-08 21:34:25 +01:00 committed by Thomas Gleixner
parent 56144737e6
commit 20d087368d
1 changed files with 12 additions and 9 deletions
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21
kernel/time/time.c
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@ -550,18 +550,21 @@ EXPORT_SYMBOL(set_normalized_timespec64);
*/
struct timespec64 ns_to_timespec64(const s64 nsec)
{
struct timespec64 ts;
struct timespec64 ts = { 0, 0 };
s32 rem;
if (!nsec)
return (struct timespec64) {0, 0};
ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
if (unlikely(rem < 0)) {
ts.tv_sec--;
rem += NSEC_PER_SEC;
if (likely(nsec > 0)) {
ts.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
ts.tv_nsec = rem;
} else if (nsec < 0) {
/*
* With negative times, tv_sec points to the earlier
* second, and tv_nsec counts the nanoseconds since
* then, so tv_nsec is always a positive number.
*/
ts.tv_sec = -div_u64_rem(-nsec - 1, NSEC_PER_SEC, &rem) - 1;
ts.tv_nsec = NSEC_PER_SEC - rem - 1;
}
ts.tv_nsec = rem;
return ts;
}