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From:   "hasegawa-hitomi@fujitsu.com" <hasegawa-hitomi@fujitsu.com>
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Subject: RE: Utime and stime are less when getrusage (RUSAGE_THREAD) is
 executed on a tickless CPU.
Thread-Topic: Utime and stime are less when getrusage (RUSAGE_THREAD) is
 executed on a tickless CPU.
Thread-Index: AddG3PD5Dm9CD2RNQ7+TrQrb7bYc8AE2Ispg
Date:   Tue, 18 May 2021 07:59:06 +0000
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Hi Ingo, Peter, Juri, and Vincent


> I found that when I run getrusage(RUSAGE_THREAD) on a tickless CPU, the u=
time and stime I get are less than the actual time, unlike when I run getru=
sage(RUSAGE_SELF) on a single thread.
> This problem seems to be caused by the fact that se.sum_exec_runtime is n=
ot 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 ad=
just 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 se=
ems to be a discrepancy with the actual time.
> Therefore, I think I should include a process to update se.sum_exec_runti=
me just before getting the information from 'current' (as in other >process=
es except RUSAGE_THREAD). I'm thinking of the following improvement.
>=20
> @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
>         if (who =3D=3D RUSAGE_THREAD) {
> +               task_sched_runtime(current);
>                 task_cputime_adjusted(current, &utime, &stime);
>=20
> Is there any possible problem with this?


Any comments?

Thanks.
Hitomi Hasegawa