How does Ubuntu handle the jiffy wraparound issue?

Shubham Saxena

1/9/24, 2:19 PM

The 64bits jiffies returned by my embedded linux system after it booted up. After 5 minutes, the return value will loop around to zero and continue to increase. will be 0xffff ffff ffff b22b.

# include <sys/times.h>
long long unsigned int tmpJiffies = times(NULL);
printf("the tmpJiffies is 0x%llx.\n", tmpJiffies);

I discovered the following code in the Linux kernel's includelinuxjiffies.h file: That is why, after 5 minutes of system bootup, the jiffies wrap around.

/*
 * 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))

However, when I attempt it on my Ubuntu linux system, the jiffies returned value differs. It begins at 0x6667bf66.

I'm curious how Ubuntu manages to achieve this.

0 + 0

syslinux

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