Here's an older thread discussing jiffies, answering the question "what are they?"

From: sting sting [email blocked]
To:  linux-kernel
Subject: short explanation -jiffies (newbie)
Date: Thu, 16 Oct 2003 21:55:22 +0200

Hello,
can someone give a short explanation what jiffies are?
regards
sting



From: Richard B. Johnson [email blocked]
Subject: Re: short explanation -jiffies (newbie)
Date: Thu, 16 Oct 2003 16:13:56 -0400 (EDT)

On Thu, 16 Oct 2003, sting sting wrote:

It is a variable that keeps increasing forever until
it wraps back to zero at which time it still keeps
increasing. It gets increased at the HZ (a defined constant)
rate as a result of a hardware interrupt.

It is used for various timing functions within the kernel.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.



From: Jesper Juhl [email blocked]
Subject: Re: short explanation -jiffies (newbie)
Date: Thu, 16 Oct 2003 23:01:37 +0200 (CEST)


On Thu, 16 Oct 2003, sting sting wrote:

> Hello,
> can someone give a short explanation what jiffies are?

A short explanation :

"Basic packet of kernel time, around 10ms on x86. Related to HZ, the basic
resolution of the operating system. The timer interrupt is raised each
10ms, which then performs some h/w timer related stuff, and marks a couple
of bh's ready to run if applicable."

is given at :

http://www.kernelnewbies.org/glossary/#J

For more details you could take a look at these files (there are more) in
the kernel source :

include/linux/delay.h
init/main.c

to find more relevant files try something like this in the kernel source
tree :

for i in `find -name *.[ch]`; do grep -H jiffy $i; done



Kind regards,

Jesper Juhl

• Archive of above thread