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Subject: [patch-mm] dynticks: Fix one off jiffy update
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Andrew Morton <akpm@osdl.org>
Cc: Karsten Wiese <fzu@wemgehoertderstaat.de>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Tue, 30 Jan 2007 00:24:43 +0100
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Sigh. /me wanted to be too clever and needs to order more brown
paperbags now.

The rework of the jiffy update code introduced a one off error, which
led to a one off accounting error for last_jiffy_update. This made
jiffies lag behind.

Noticed by Karsten Wiese (cpufreq_ondemand weirdness).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Index: linux-2.6.20-rc6-mm/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.20-rc6-mm.orig/kernel/time/tick-sched.c
+++ linux-2.6.20-rc6-mm/kernel/time/tick-sched.c
@@ -43,7 +43,7 @@ struct tick_sched *tick_get_tick_sched(i
  */
 static void tick_do_update_jiffies64(ktime_t now)
 {
-	unsigned long ticks = 1;
+	unsigned long ticks = 0;
 	ktime_t delta;
 
 	/* Reevalute with xtime_lock held */
@@ -60,12 +60,12 @@ static void tick_do_update_jiffies64(kti
 		if (unlikely(delta.tv64 >= tick_period.tv64)) {
 			s64 incr = ktime_to_ns(tick_period);
 
-			ticks += ktime_divns(delta, incr);
+			ticks = ktime_divns(delta, incr);
 
 			last_jiffies_update = ktime_add_ns(last_jiffies_update,
 							   incr * ticks);
 		}
-		do_timer(ticks);
+		do_timer(++ticks);
 	}
 	write_sequnlock(&xtime_lock);
 }