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From:   Thomas Gleixner <tglx@linutronix.de>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Anna-Maria Behnsen <anna-maria@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Artem Savkov <asavkov@redhat.com>
Subject: timers: Simplify calc_index()
Date:   Mon, 04 Apr 2022 16:47:55 +0200
Message-ID: <87h778j46c.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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);
 }