linux-kernel - [PATCH 23/24] jrcu: better timer slop

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Date:	Thu, 24 Mar 2011 13:48:04 -0400
From:	Joe Korty <joe.korty@...r.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	fweisbec@...il.com, peterz@...radead.org, laijs@...fujitsu.com,
	mathieu.desnoyers@...icios.com, dhowells@...hat.com,
	loic.minier@...aro.org, dhaval.giani@...il.com, tglx@...utronix.de,
	josh@...htriplett.org, houston.jim@...cast.net,
	andi@...stfloor.org, linux-kernel@...r.kernel.org
Subject: [PATCH 23/24] jrcu: better timer slop

jrcu: fix broken timer slop

The expression

	USEC_PER_SEC / (HZ * 3 / 2)

was trying to define a period, in usec, some 50% larger
than the natural HZ period.  Instead it made a period
some 30% shorter.

But such attempts are completely unnecessary.  HZ alone
works just fine.

Signed-off-by: Joe Korty <joe.korty@...r.com>

Index: b/kernel/jrcu.c
===================================================================
--- a/kernel/jrcu.c
+++ b/kernel/jrcu.c
@@ -131,7 +131,7 @@ static struct rcu_stats {
 
 #define RCU_HZ			(20)
 #define RCU_HZ_PERIOD_US	(USEC_PER_SEC / RCU_HZ)
-#define RCU_HZ_DELTA_US		(USEC_PER_SEC / (HZ * 3 / 2))
+#define RCU_HZ_DELTA_US		(USEC_PER_SEC / HZ)
 
 static int rcu_hz = RCU_HZ;
 static int rcu_hz_period_us = RCU_HZ_PERIOD_US;
--
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