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Need your help on setting of INITIAL_JIFFIES

To: <sshtylyov@ru.mvista.com>, <hvr@gnu.org>, <linux-mips@linux-mips.org>, <clem.taylor@gmail.com>, <linux-mips-bounce@linux-mips.org>, <4468F40F.80902@ru.mvista.com>, <4468EE9B.4000009@ru.mvista.com>
Subject: Need your help on setting of INITIAL_JIFFIES
From: "MOHANTY CHANDAN-WJKD64" <chandanmohanty@motorolasolutions.com>
Date: Fri, 20 May 2011 09:09:23 +0100
Cc: "MOHANTY CHANDAN-WJKD64" <chandanmohanty@motorolasolutions.com>
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Thread-topic: Need your help on setting of INITIAL_JIFFIES
Hi,
My greetings to all the enlightened Linux Souls.
 
 I got all the mail ids from one of Linux based mail chain/URL  http://www.linux-mips.org/archives/linux-mips/2006-05/msg00193.html
 
Pls guide me on the usage of  INITIAL_JIFFIES.
 
 
 
 
In the source of linux kernel \include\linux\jiffies.h there is code like this
 
/*
 * Have the 32 bit jiffies value wrap 5 minutes after boot
 * so jiffies wrap bugs show up earlier.
 */
#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
 
 
 This sets the initial jiffies value to 0x00000000fffb6c20, which can trigger 32-bit wraparound bugs .It is an offset to the jiffies counter,so that it begins from a large value instead of zero. So the wrap-around happens
earlier,making it possible to detect any counter wrap-around bugs much quicker regardless of the HZ setting.
 
 
 
 
1.Suppose I want to simulate the jiffies wraparound after 30 mins(1800sec) of reboot.Can I change code as below in kernel?
 
#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-1800*HZ))
u64 jiffies_64 = INITIAL_JIFFIES;
 
 
2.How to verify/test that wraparound has happened?
 
 
Regards
Chandan
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