linux-kernel - Re: 2.6.32.2: undefined reference to `_

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Message-ID: <20091221122121.6853d68c@nehalam>
Date:	Mon, 21 Dec 2009 12:21:21 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Mike Garrison <mcgarr@...ch.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Corrado Zoccolo <czoccolo@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.32.2: undefined reference to `__udivdi3'

The new menu governor driver is written by Intel folks who never use 32-bit
anymore it seems :-)
---------------------------------------------------------
Subject: [PATCH] menu: use proper 64 bit math

The new menu governor is incorrectly doing a 64 bit divide.
Compile tested only

Signed-off-by: Stephen Hemminger <shemminger@...tta.com>

--- a/drivers/cpuidle/governors/menu.c	2009-12-21 12:02:25.840083589 -0800
+++ b/drivers/cpuidle/governors/menu.c	2009-12-21 12:16:42.418834255 -0800
@@ -18,6 +18,7 @@
 #include <linux/hrtimer.h>
 #include <linux/tick.h>
 #include <linux/sched.h>
+#include <linux/math64.h>
 
 #define BUCKETS 12
 #define RESOLUTION 1024
@@ -169,6 +170,12 @@ static DEFINE_PER_CPU(struct menu_device
 
 static void menu_update(struct cpuidle_device *dev);
 
+/* This implements DIV_ROUND_CLOSEST but avoids 64 bit division */
+static u64 div_round64(u64 dividend, u32 divisor)
+{
+	return div_u64(dividend + (divisor / 2), divisor);
+}
+
 /**
  * menu_select - selects the next idle state to enter
  * @dev: the CPU
@@ -209,9 +216,8 @@ static int menu_select(struct cpuidle_de
 		data->correction_factor[data->bucket] = RESOLUTION * DECAY;
 
 	/* Make sure to round up for half microseconds */
-	data->predicted_us = DIV_ROUND_CLOSEST(
-		data->expected_us * data->correction_factor[data->bucket],
-		RESOLUTION * DECAY);
+	data->predicted_us = div_round64(data->expected_us * data->correction_factor[data->bucket],
+					 RESOLUTION * DECAY);
 
 	/*
 	 * We want to default to C1 (hlt), not to busy polling
--
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