Re: [patch v2 4/4] taskstats: Export "cdata_wait" CPU times with taskstats

[Oleg Nesterov <oleg@redhat.com>]

Oh, sorry for the delay. Again ;)

On 12/02, Michael Holzheu wrote:
>
> 1) You have a thread group with several threads
> 2) Thread group leader dies and reports cdata_wait in taskstats_exit()
> 3) Thread group leader stays around as zombie until the thread
>    group dies
> 4) Other forked processes of this thread group die
> 5) cdata_wait of thread group is increased
> 6) The new cdata is not reported by any exit event of the thread group

Yes.

> So maybe we should remove the thread_group_leader() check and report
> cdata_wait for all threads and not only for the thread group leader? We
> also should add ac_tgid to taskstats so that userspace can find the
> corresponding thread group for each thread.

I do not know. My only point was, this thread_group_leader() looks
a bit confusing, at least if we are talking about do_exit() path.

> When the last thread exits and the process/thread group dies,
> taskstats_exit() sends an additional taskstats struct to userspace that
> aggregates the thread accounting data. Currently only the delay
> accounting data is aggregated (see
> taskstats_exit->fill_tgid_exit->delayacct_add_tsk). Not sure, why the
> other information is not aggregated. We perhaps also should include
> ac_cXtime in the aggregated taskstats.

Not sure I understand... Do you mean

	if (is_thread_group)
		fill_tgid_exit(tsk);

? Afaics, this is not "When the last thread exits", this is
"this program is multithreaded, it has (or had) other threads".

Oleg.