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

[Dmitry Safonov]

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@xxxxxxxxxx>
---
 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