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

[Michael Holzheu]

On Wed, 2010-12-01 at 19:51 +0100, Oleg Nesterov wrote:
> But in fact I don't really understand this anyway. This is called
> before we reparent our children. This means that ac_cutime/ac_cstime
> can be changed after that (multithreading, or full_cdata_enabled).
> 
> Say, taskstats_exit()->fill_stats()->bacct_add_tsk(). Every thread
> does this, including the group_leader. But, it is possible that
> group_leader exits first, before other threads. IOW, what
> stats->ac_cXtime actually mean?

Because I worked mostly with the ptop tool, I was not so much focused on
the taskstats exit events, but instead more on the taskstats commands to
query data for running tasks.

For the query scenario stats->ac_cXtime means:

1) full_cdata=0: "Sum of CPU time of exited child processes where
   sys_wait() have been done (up to this time)"
2) full_cdata=1: "Sum of CPU time of exited child processes where
   sys_wait() have been done plus exited child processes where
   the parents ignored SIGCHLD or have set SA_NOCLDWAIT (up to
   this time)"

Regarding taskstats_exit(): Do you have something like the following
scenario in mind?

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

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.

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.

Michael



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/