Jiffies - how to calculate seconds elapsed?

Question

I have a piece of code, i want to calculate the time in seconds.. though i am getting time in jiffies, how can i convert it in seconds?

here is my kernel code:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/timer.h>
unsigned long js, je, tet;
int netblock_init_module(void){
    js = jiffies;
    printk("\n[Jiffies start Time : %lu]\nModule Started.\n", js);
    return 0;
}

void netblock_cleanup_module(void) {
    je = jiffies;
    printk("\n[Jiffies End Time : %lu]\nModule Removed.\n", je);
    tet = je - js;
    printk("\nEnd Time [%lu] - Start Time [%lu]: \nTotlal elapsed Time [%lu]\n",js,je, tet);

}

module_init(netblock_init_module);
module_exit(netblock_cleanup_module);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("JIFFIES EXAMPLE");
MODULE_AUTHOR("RAHEEL");

Output I am getting is like to this:

$insmod jiffexample.ko

[Jiffies start Time : 13363583]

Module Started

$rmmod jiffexample.ko

[Jiffies End Time : 13361588]

Module Removed.

End Time 13361588 - Start Time 1336358

Total Elapsed time [1605]

Now i want to get converted time in seconds.. how its possible to convert this elapsed time 1605 in seconds? or alternatively can you please tell me how many jiffies are in a second?

Solution 1

For your use case, you can use either:

jiffies_to_msecs or jiffies_to_usecs

---

All conversion routines below:

From include/linux/jiffies.h

...
/*
 * Convert various time units to each other:
 */
extern unsigned int jiffies_to_msecs(const unsigned long j);
extern unsigned int jiffies_to_usecs(const unsigned long j);
extern unsigned long msecs_to_jiffies(const unsigned int m);
extern unsigned long usecs_to_jiffies(const unsigned int u);
extern unsigned long timespec_to_jiffies(const struct timespec *value);
extern void jiffies_to_timespec(const unsigned long jiffies,
                            struct timespec *value);
extern unsigned long timeval_to_jiffies(const struct timeval *value);
extern void jiffies_to_timeval(const unsigned long jiffies,
                           struct timeval *value);
extern clock_t jiffies_to_clock_t(unsigned long x);
extern unsigned long clock_t_to_jiffies(unsigned long x);
extern u64 jiffies_64_to_clock_t(u64 x);
extern u64 nsec_to_clock_t(u64 x);
extern u64 nsecs_to_jiffies64(u64 n);
extern unsigned long nsecs_to_jiffies(u64 n);
...

Solution 2

From http://www.kernel.org/doc/man-pages/online/pages/man7/time.7.html:

The size of a jiffy is determined by the value of the kernel constant HZ.

The value of HZ varies across kernel versions and hardware platforms. On i386 the situation is as follows: on kernels up to and including 2.4.x, HZ was 100, giving a jiffy value of 0.01 seconds; starting with 2.6.0, HZ was raised to 1000, giving a jiffy of 0.001 seconds. Since kernel 2.6.13, the HZ value is a kernel configuration parameter and can be 100, 250 (the default) or 1000, yielding a jiffies value of, respectively, 0.01, 0.004, or 0.001 seconds. Since kernel 2.6.20, a further frequency is available: 300, a number that divides evenly for the common video frame rates (PAL, 25 HZ; NTSC, 30 HZ).

Just divide by HZ.