timers: Simplify calc_index()

timers: Simplify calc_index()

[Thomas Gleixner]

The level granularity round up of calc_index() does:

   (x + (1 << n)) >> n

which is obviously equivalent to

   (x >> n) + 1

but compilers can't figure that out despite the fact that the input range
is known to not cause an overflow. It's neither intuitive to read.

Just write out the obvious.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/timer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -502,7 +502,7 @@ static inline unsigned calc_index(unsign
 	 *
 	 * Round up with level granularity to prevent this.
 	 */
-	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
+	expires = (expires >> LVL_SHIFT(lvl)) + 1;
 	*bucket_expiry = expires << LVL_SHIFT(lvl);
 	return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }

[tip: timers/core] timers: Simplify calc_index()

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     a2026e44eff5d74a83d7ffee6325a007bef85385
Gitweb:        https://git.kernel.org/tip/a2026e44eff5d74a83d7ffee6325a007bef85385
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 04 Apr 2022 16:47:55 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sat, 09 Apr 2022 22:19:39 +02:00

timers: Simplify calc_index()

The level granularity round up of calc_index() does:

   (x + (1 << n)) >> n

which is obviously equivalent to

   (x >> n) + 1

but compilers can't figure that out despite the fact that the input range
is known to not cause an overflow. It's neither intuitive to read.

Just write out the obvious.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/87h778j46c.ffs@tglx

---
 kernel/time/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 204d6cd..60aebf2 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -502,7 +502,7 @@ static inline unsigned calc_index(unsigned long expires, unsigned lvl,
 	 *
 	 * Round up with level granularity to prevent this.
 	 */
-	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
+	expires = (expires >> LVL_SHIFT(lvl)) + 1;
 	*bucket_expiry = expires << LVL_SHIFT(lvl);
 	return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }