lkml.org 
[lkml]   [2019]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/8] timekeeping: optimize ns_to_timespec64
Date
I noticed that 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.

This open-codes the div_s64_rem() function here, so we can pass
a constant divider into the optimized div_u64_rem() function.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
kernel/time/time.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/kernel/time/time.c b/kernel/time/time.c
index 5c54ca632d08..45a358953f09 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -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;
}
--
2.20.0
\
 
 \ /
  Last update: 2019-11-08 21:36    [W:0.867 / U:7.028 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site