Need your help on setting of INITIAL_JIFFIES

["MOHANTY CHANDAN-WJKD64" <chandanmohanty@motorolasolutions.com>]

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