Hello again. I have the following code: ======================================== clock_t c_sum, j, p; cputime_t j_tmp; ... c_sum = cputime64_to_clock_t(task->utime) + cputime64_to_clock_t(task->stime); cur_j = jiffies; j_tmp = jiffies64_to_cputime64(cur_j); j = cputime64_to_clock_t(j_tmp); p = (c_sum * 100) / j; ======================================== And if I check the p value of a certain process it gives wrong results. For example for a process using 99% of the CPU it shows 20. What am I doing wrong? Greets, Luka Erik Mouw pravi: > On Fri, Aug 24, 2007 at 03:18:32AM +0200, Luka Napotnik wrote: >> I'm new to kernel development and have some questions. > >> 1. Apperently kernel doesn't support operations with floating-point >> types. How can I then divide a number 265 with the number 7 if I can >> divide only by 2 with right-shifting? > > Correct, floating point arithmetic is not allowed in the kernel. Use > fixed point math if you really need more precision. Or export the raw > values to userland and do the floating point math over there. > >> 2. I'm trying to get the percentage of CPU used for a certain >> task_struct and figured the following formula: > >> (task->utime + task->stime) / jiffies > >> Before calculating I convert all the variables to jiffies. Is this correct? > > That should be ok. Couple of things: > > - jiffies is continuously updated, so your percentage formula doesn't > work. you need to use a jiffies difference > - jiffies can and will wrap around > > But why would you calculate this in kernel? All the information is > already exported to userland so do the calculations over there. Get the > source for "top" and see how it is done. > > > Erik > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
