Converting jiffies to milli seconds

Question

How do I manually convert jiffies to milliseconds and vice versa in Linux? I know kernel 2.6 has a function for this, but I\'m working on 2.4 (homework) and though I looked

Answer 1

Jiffies are hard-coded in Linux 2.4. Check the definition of HZ, which is defined in the architecture-specific param.h. It's often 100 Hz, which is one tick every (1 sec/100 ticks * 1000 ms/sec) 10 ms.

This holds true for i386, and HZ is defined in include/asm-i386/param.h.

There are functions in include/linux/time.h called timespec_to_jiffies and jiffies_to_timespec where you can convert back and forth between a struct timespec and jiffies:

    #define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)

    static __inline__ unsigned long
    timespec_to_jiffies(struct timespec *value)
    {
            unsigned long sec = value->tv_sec;
            long nsec = value->tv_nsec;

            if (sec >= (MAX_JIFFY_OFFSET / HZ))
                    return MAX_JIFFY_OFFSET;
            nsec += 1000000000L / HZ - 1;
            nsec /= 1000000000L / HZ;
            return HZ * sec + nsec;
    }

    static __inline__ void
    jiffies_to_timespec(unsigned long jiffies, struct timespec *value)
    {
            value->tv_nsec = (jiffies % HZ) * (1000000000L / HZ);
            value->tv_sec = jiffies / HZ;
    }

Note: I checked this info in version 2.4.22.