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Date: Mon, 6 Dec 2010 20:45:50 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Shailabh Nagar <nagar1234@in.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
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        Roland McGrath <roland@redhat.com>, Valdis.Kletnieks@vt.edu,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [patch v2 4/4] taskstats: Export "cdata_wait" CPU times with
 taskstats
Message-ID: <20101206151550.GF3158@balbir.in.ibm.com>
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* Michael Holzheu <holzheu@linux.vnet.ibm.com> [2010-12-06 13:37:37]:

> Hello Balbir,
> 
> On Fri, 2010-12-03 at 13:03 +0530, Balbir Singh wrote:
> > * Oleg Nesterov <oleg@redhat.com> [2010-12-01 19:51:28]:
> > 
> > > On 11/29, Michael Holzheu wrote:
> [snip]
> > > 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?
> > > 
> > 
> > stats->ac_* time was designed only for tgid's to begin with,
> 
> You mean for tids (threads/tasks), no? stats->ac_* time is only reported
> for threads in bacct_add_tsk() and not for tgids.

Sorry, I meant tid's or pid

> 
> > so I am
> > not sure if ac_cXtime makes sense for threads
> 
> I would suggest to do it the same way as /proc/<tgid>/tasks/<tid>/stat.
> It reports the (same) cumulative time for each thread. See
> do_task_stat() in fs/proc/array.c. So IMHO also for taskstats it makes
> sense to include the cXtime for all threads and not only for the thread
> group leader. 
> 
> Also I would include tgid in taskstats so that userspace can group the
> tasks into thread groups. 
> 
> I am not sure regarding the aggregation for tgids in
> TASKSTATS_CMD_ATTR_TGID and exit events with group_dead=1. Currently
> only the delay accounting numbers are aggregated. If we would do it
> like /proc/<tgid>/stat (do_task_stat() with whole=1) we also could
> aggregate also the other values e.g. the CPU time.
> 
> I think the following tgid data would make sense to be returned for
> TASKSTATS_CMD_ATTR_TGID and exit events with group_dead=1:
> 
> bacct_add_tsk():
> ----------------
> ac_pid         thread group leader (tsk->tgid)
> ac_etime       thread group leader
> ac_btime       thread group leader
> ac_nice        thread group leader
> ac_sched       thread group leader
> ac_uid         thread group leader
> ac_gid         thread group leader
> ac_ppid        thread group leader
> ac_comm        thread group leader
> ac_exit_code   thread group leader
> ac_flags       thread group leader
> ac_utimescaled ??
> ac_stimescaled ??
> ac_utime       sum for all live threads + cdata_threads
> ac_stime       sum for all live threads + cdata_threads
> ac_minflt      sum for all live threads + cdata_threads
> ac_majflt      sum for all live threads + cdata_threads
> 
> new:
> ac_cutime      cdata_wait
> ac_cstime      cdata_wait
> ac_tgid        thread group leader
>

This seems to be make sense.
 
> xacct_add_tsk():
> ----------------
> coremem        ?
> virtmem        ?
> hiwater_rss    thread group leader
> hiwater_vm     thread group leader
> read_char      sum for all live threads + tsk->signal.ioac
> write_char     sum for all live threads + tsk->signal.ioac
> read_syscalls  sum for all live threads + tsk->signal.ioac
> write_syscalls sum for all live threads + tsk->signal.ioac
> read_bytes     sum for all live threads + tsk->signal.ioac
> write bytes    sum for all live threads + tsk->signal.ioac
> cancelled_write_bytes sum for all live threads + tsk->signal.ioac
>   
> If we leave everything as it currently is for tgid accounting, we
> probably should also not include the cXtime for tgids and just include
> the data for threads (TASKSTATS_CMD_ATTR_PID and task exit events).
> 
> What do you think?
>

This makes sense to me, we'd need to bump up the API version if we are
going to make this change. 

-- 
	Three Cheers,
	Balbir
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