[PATCH 4/9] select: Micro-optimise __estimate_accuracy()

Dmitry Safonov
2019-09-09T10:23:54Z

Shift on s64 is faster than division, use it instead.

As the result of the patch there is a hardly user-visible effect:
poll(), select(), etc syscalls will be a bit more precise on ~2.3%
than before because 1000 != 1024 :)

Signed-off-by: Dmitry Safonov <dima@arista.com>
---
fs/select.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 12cdefd3be2d..2477c202631e 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -51,15 +51,14 @@

static long __estimate_accuracy(ktime_t slack)
{
- int divfactor = 1000;
-
if (slack < 0)
return 0;

- if (task_nice(current) > 0)
- divfactor = divfactor / 5;
+ /* A bit more precise than 0.1% */
+ slack = slack >> 10;

- slack = ktime_divns(slack, divfactor);
+ if (task_nice(current) > 0)
+ slack = slack * 5;

if (slack > MAX_SLACK)
return MAX_SLACK;
--
2.23.0