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Old 04-10-2004, 01:21 PM   #1
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Registered: Apr 2004
Posts: 2

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questions about reference to "jiffies"

sorry I am a linux newbie ,
I want to reference the extern variable "jiffies" value updated by kernel
in my programming code , but I found error message at compiled time , I don't know which header files should be included correctly, or maybe some where goes wrong . Can someone teach me how to reference the "jiffies" anywhere in my code !!

help would be greatly appreciated.
Thank you in advance

my test.c file
#include <stdio.h>
#include <linux/timer.h>
#include <linux/times.h>
#include <linux/timex.h>
#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <asm/uaccess.h>
extern unsigned long volatile jiffies;

int gett(void);

main ()
int result;
result = gett();
printf("result is %d\n", result);
printf("jiffies %.3lg \n", jiffies);
int gett(void){
int mult[2];
puts("puts multi a & b");
scanf("%d", &mult[0]);
scanf("%d", &mult[1]);
return mult[0]*mult[1];

my makefile
INCLUDE = /usr/src/linux/include/
TARGET = test
CC = gcc
SRC = test.c


$(CC) -I$(INCLUDE) -o $(TARGET) $(SRC)

Old 04-10-2004, 01:38 PM   #2
Registered: Mar 2004
Location: Massachusetts
Distribution: Debian
Posts: 557

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I don't think jiffies is available to userspace at all -- you'd have to write a kernel module to get ad it.
Old 04-10-2004, 02:52 PM   #3
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Registered: Apr 2004
Posts: 2

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So if I want to estimate how long a code segment or a single function takes when called , by what manner or functions is recommanded while I can get the estimated time from entring it to leaving it , measured in micro second or even precisely ?
Old 04-10-2004, 03:15 PM   #4
Registered: Mar 2004
Location: Massachusetts
Distribution: Debian
Posts: 557

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clock_gettime() looks promising, and there's gettimeofday(). I'm not sure if either of those will really give microsecond precision -- they may be limited to 1/HZ.

If you're benchmarking something with a short running time, you should run it many times and divide, rather than trying to time just one run.
Old 04-12-2004, 10:16 AM   #5
Registered: Jul 2003
Location: bangalore . india
Distribution: openSUSE 10.3
Posts: 251

Rep: Reputation: 33
there are various tools to do this ...gprof for one does that...profiles how much time is spent in what part of code...youd have to compile your code with -pg option for code to enable profiling...

or what aluser says is gettimeofday...

also dont include the kernel space header files...
use the default /usr/include header files..
these are the files meant for the user space stuff....


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