RE: Utime and stime are less when getrusage (RUSAGE_THREAD) is executed on a tickless CPU.

["hasegawa-hitomi@fujitsu.com" <hasegawa-hitomi@fujitsu.com>]

Hi Ingo, Peter, Juri, and Vincent


> I found that when I run getrusage(RUSAGE_THREAD) on a tickless CPU, the utime and stime I get are less than the actual time, unlike when I run getrusage(RUSAGE_SELF) on a single thread.
> This problem seems to be caused by the fact that se.sum_exec_runtime is not updated just before getting the information from 'current'.
> In the current implementation, task_cputime_adjusted() calls task_cputime() to get the 'current' utime and stime, then calls cputime_adjust() >to adjust the sum of utime and stime to be equal to cputime.sum_exec_runtime. On a tickless CPU, sum_exec_runtime is not updated >periodically, so there seems to be a discrepancy with the actual time.
> Therefore, I think I should include a process to update se.sum_exec_runtime just before getting the information from 'current' (as in other >processes except RUSAGE_THREAD). I'm thinking of the following improvement.
> 
> @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
>         if (who == RUSAGE_THREAD) {
> +               task_sched_runtime(current);
>                 task_cputime_adjusted(current, &utime, &stime);
> 
> Is there any possible problem with this?


Any comments?

Thanks.
Hitomi Hasegawa