From: Oleg Nesterov <oleg@redhat.com>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Shailabh Nagar <nagar1234@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Venkatesh Pallipadi <venki@google.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Suresh Siddha <suresh.b.siddha@intel.com>,
John stultz <johnstul@us.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Balbir Singh <balbir@linux.vnet.ibm.com>,
Ingo Molnar <mingo@elte.hu>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 09/10] taskstats: Fix exit CPU time accounting
Date: Tue, 19 Oct 2010 16:17:25 +0200 [thread overview]
Message-ID: <20101019141725.GA32361@redhat.com> (raw)
In-Reply-To: <1287153246.1896.231.camel@holzheu-laptop>
On 10/15, Michael Holzheu wrote:
>
> On Thu, 2010-10-14 at 15:47 +0200, Oleg Nesterov wrote:
>
> > Yes. But __account_to_parent() always sets p->exit_accounting_done = 1.
> > And __exit_signal() calls __account_to_parent() only if it is not set.
> >
> > This means that we update either cdata_wait (if the child was reaped
> > by parent) or cdata_acct (the process auto-reaps itself).
>
> No. The accounting of cdata_acct is done unconditionally in
> __account_to_parent(). It is done for both cases wait=0 and wait=1,
> therefore no CPU time gets lost. Accounting of cdata_wait is done only
> on the sys_wait() path, where "wait" is "1".
Ah, got it, I didn't notice this detail.
Thanks.
> I think it works as it currently is. But as already said, this probably
> could be done better. At least your confusion seems to prove that :-)
Perhaps ;)
To me, it would be cleaner and simpler if you kill ->exit_accounting_done.
Both wait_task_zombie() and __exit_signal() could just call
__account_to_parent(parent_for_accounting) unconditionally passing
either real_parent or acct_parent as an argument. This also saves a
word in task_struct.
> de_thread() is also a very interesting spot for accounting. The thread
> that calls exec() gets a bit of the identity of the old thread group
> leader e.g. PID and start time, but it keeps the old CPU times. This
> looks strange to me.
Well, the main thread represents the whole process for ps/etc, that
is why we update ->start_time.
But,
> Wouldn't it be better to either exchange the accounting data between old
> and new leader
I dunno. The exiting old leader will update sig->utime/etc, so we do not
lose this info from the "whole process" pov. But yes, if user-space
looks at the single thread with that TGID it can notice that, say, utime
goes backward.
> or add the current accounting data of the new leader to
> the signal struct and initialize them with zero again?
Sorry, I don't understand this "initialize them with zero". What
is "them" ?
> > I think you can simplify this, but I am not sure right now.
> >
> > First of all, ->acct_parent should be moved from task_struct to
> > signal_struct. No need to initialize t->acct_parent unless t is
> > the group leader (this means we can avoid do/while_each_thread
> > loop during re-parenting, but de_thread needs another trivial
> > change).
> > No need to change forget_original_parent() at all, instead we
> > can the single line
> >
> > p->signal->acct_parent = father->signal->acct_parent;
> >
> > to reparent_leader(), after the "if (same_thread_group())" check.
> >
> > What do you think?
>
> I think it is not that easy because we still have to maintain the
> children_acct list. This list is used to reparent all the accounting
> children to the new accounting parent.
Yes, sure, reparent_leader() should also do list_move_tail(acct_sibling),
I forget to mention this.
I guess you already understand this, but just in case. Please look at
sibling/children relationship. We do not add the sub-threads on
->children list, only the main thread.
However, every thread has its own ->parent and ->children, this is
because we have __WNOTHREAD. But acct-parenting doesn't have this
problem, only the main thread needs the properly initialized
->acct_parent, it is never needed until the whole process dies.
> But in principle you are right that acct_parent could be moved to the
> signal_struct because we only have to change it, when a thread group
> leader dies.
Yes. And if we move it into signal_struct, then we shouldn't worry
about updating it in de_thread().
However, de_thread() should do list_replace_init(leader->acct_sibling)
to add the new leader to acct_children.
I am not sure this really makes sense, but in fact you can move
->acct_sibling and ->acct_childen from task_struct to signal_struct
as well, note that you can trivially find the group leader looking
at signal->leader_pid. (actually, ->group_leader should be moved
to signal_struct, but this is another story). In this case de_thread()
needs no changes, and we save the space in task_struct.
Oleg.
next prev parent reply other threads:[~2010-10-19 14:22 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-23 13:48 [RFC][PATCH 00/10] taskstats: Enhancements for precise accounting Michael Holzheu
2010-09-23 14:00 ` [RFC][PATCH 01/10] taskstats: Use real microsecond granularity for CPU times Michael Holzheu
2010-10-07 5:08 ` Balbir Singh
2010-10-08 15:08 ` Michael Holzheu
2010-10-08 16:39 ` Balbir Singh
2010-09-23 14:01 ` [RFC][PATCH 02/10] taskstats: Separate taskstats commands Michael Holzheu
2010-09-27 9:32 ` Balbir Singh
2010-10-11 7:40 ` Balbir Singh
2010-09-23 14:01 ` [RFC][PATCH 03/10] taskstats: Split fill_pid function Michael Holzheu
2010-09-23 17:33 ` Oleg Nesterov
2010-09-27 9:33 ` Balbir Singh
2010-10-11 8:31 ` Balbir Singh
2010-09-23 14:01 ` [RFC][PATCH 04/10] taskstats: Add new taskstats command TASKSTATS_CMD_ATTR_PIDS Michael Holzheu
2010-09-23 14:01 ` [RFC][PATCH 05/10] taskstats: Add "/proc/taskstats" Michael Holzheu
2010-09-23 14:01 ` [RFC][PATCH 06/10] taskstats: Add thread group ID to taskstats structure Michael Holzheu
2010-09-23 14:01 ` [RFC][PATCH 07/10] taskstats: Add per task steal time accounting Michael Holzheu
2010-09-23 14:02 ` [RFC][PATCH 08/10] taskstats: Add cumulative CPU time (user, system and steal) Michael Holzheu
2010-09-23 14:02 ` [RFC][PATCH 09/10] taskstats: Fix exit CPU time accounting Michael Holzheu
2010-09-23 17:10 ` Oleg Nesterov
2010-09-24 12:18 ` Michael Holzheu
2010-09-26 18:11 ` Oleg Nesterov
2010-09-27 13:23 ` Michael Holzheu
2010-09-27 13:42 ` Martin Schwidefsky
2010-09-27 16:51 ` Oleg Nesterov
2010-09-28 7:09 ` Martin Schwidefsky
2010-09-29 19:19 ` Roland McGrath
2010-09-30 13:47 ` Michael Holzheu
2010-10-05 8:57 ` Roland McGrath
2010-10-06 9:29 ` Michael Holzheu
2010-10-06 15:26 ` Oleg Nesterov
2010-10-07 15:06 ` Michael Holzheu
2010-10-11 12:37 ` Oleg Nesterov
2010-10-12 13:10 ` Michael Holzheu
2010-10-14 13:47 ` Oleg Nesterov
2010-10-15 14:34 ` Michael Holzheu
2010-10-19 14:17 ` Oleg Nesterov [this message]
2010-10-22 16:53 ` Michael Holzheu
2010-09-28 8:36 ` Balbir Singh
2010-09-28 9:08 ` Martin Schwidefsky
2010-09-28 9:23 ` Balbir Singh
2010-09-28 10:36 ` Martin Schwidefsky
2010-09-28 10:39 ` Balbir Singh
2010-09-28 8:21 ` Balbir Singh
2010-09-28 16:50 ` Michael Holzheu
2010-09-23 14:04 ` [RFC][PATCH 10/10] taststats: User space with ptop tool Michael Holzheu
2010-09-23 20:11 ` [RFC][PATCH 00/10] taskstats: Enhancements for precise accounting Andrew Morton
2010-09-23 22:11 ` Matt Helsley
2010-09-24 12:39 ` Michael Holzheu
2010-09-25 18:19 ` Serge E. Hallyn
2010-09-24 9:10 ` Michael Holzheu
2010-09-24 18:50 ` Andrew Morton
2010-09-27 9:18 ` Michael Holzheu
2010-09-27 20:02 ` Andrew Morton
2010-09-28 8:17 ` Balbir Singh
2010-09-27 10:49 ` Balbir Singh
2010-09-24 9:16 ` Balbir Singh
2010-09-30 8:38 ` Andi Kleen
2010-09-30 13:56 ` Michael Holzheu
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