linux-kernel - [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit variable conversion

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Date:	Wed, 10 Aug 2016 08:14:52 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org
Cc:	bsegall@...gle.com, pjt@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
	Yuyang Du <yuyang.du@...el.com>
Subject: [PATCH v1 07/10] sched/fair: Remove useless 64-bit to 32-bit variable conversion

In __decay_sum(), the 64-bit to 32-bit variable conversion makes no
performance nor correctness use.

Minor cleanup and no functionality change.

Signed-off-by: Yuyang Du <yuyang.du@...el.com>
---
 kernel/sched/fair.c |   13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 283e2c2..eea3349 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2616,16 +2616,11 @@ static const u32 __accumulated_sum_N32[] = {
  */
 static __always_inline u64 __decay_sum(u64 val, u64 n)
 {
-	unsigned int local_n;
-
 	if (!n)
 		return val;
 	else if (unlikely(n > SCHED_AVG_HALFLIFE * 63))
 		return 0;
 
-	/* after bounds checking we can collapse to 32-bit */
-	local_n = n;
-
 	/*
 	 * As y^HALFLIFE = 1/2, we can combine
 	 *    y^n = 1/2^(n/HALFLIFE) * y^(n%HALFLIFE)
@@ -2633,12 +2628,12 @@ static __always_inline u64 __decay_sum(u64 val, u64 n)
 	 *
 	 * To achieve constant time __decay_load.
 	 */
-	if (unlikely(local_n >= SCHED_AVG_HALFLIFE)) {
-		val >>= local_n / SCHED_AVG_HALFLIFE;
-		local_n %= SCHED_AVG_HALFLIFE;
+	if (unlikely(n >= SCHED_AVG_HALFLIFE)) {
+		val >>= n / SCHED_AVG_HALFLIFE;
+		n %= SCHED_AVG_HALFLIFE;
 	}
 
-	val = mul_u64_u32_shr(val, __decay_inv_multiply_N[local_n], 32);
+	val = mul_u64_u32_shr(val, __decay_inv_multiply_N[n], 32);
 	return val;
 }
 
-- 
1.7.9.5