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: Wed, 6 Oct 2010 17:26:09 +0200 [thread overview]
Message-ID: <20101006152609.GA21169@redhat.com> (raw)
In-Reply-To: <1286357350.1888.25.camel@holzheu-laptop>
I didn't read the whole patch, but some parts doesn't look right,
On 10/06, Michael Holzheu wrote:
>
> The patch also approaches another ugly Unix behavior regarding process
> accounting. If a parent process dies before his children, the children
> get the reaper process (init) as new parent. If we want to determine the
> CPU usage of a process tree with cumulative time, this is very
> suboptimal. To fix this I added a new process relationship tree for
> accounting.
Well, I must admit, I can't say I like the complications this change adds ;)
In any case, imho this change needs a separate patch/discussion.
> Besides of that the patch adds an "acct_parent" pointer next to the parent
> pointer and a "children_acct" list next to the children list to the
> task_struct in order to remember the correct accounting task relationship.
I am not sure I understand the "correct accounting" above. ->acct_parent
adds the "parallel" hierarchy. In the simplest case, suppose that some
process P forks the child C and exits. Then C->acct_parent == P->real_parent
(P->acct_parent in general). I am not sure this is always good.
Anyway,
> @@ -90,6 +156,24 @@ static void __exit_signal(struct task_st
>
> posix_cpu_timers_exit(tsk);
> if (group_dead) {
> + if (!tsk->exit_accounting_done) {
> +#ifdef __s390x__
> + /*
> + * FIXME: On s390 we can call account_process_tick to update
> + * CPU time information. This is probably not valid on other
> + * architectures.
> + */
> + if (current == tsk)
> + account_process_tick(current, 1);
> +#endif
> + /*
> + * FIXME: This somehow has to be moved to
> + * finish_task_switch(), because otherwise
> + * if the process accounts itself, the CPU time
> + * that is used for this code will be lost.
> + */
> + __account_to_parent(tsk, 0);
We hold the wrong ->siglock here.
Also, the logic behind ->exit_accounting_done looks wrong (and unneeded)
but I am not sure...
> @@ -772,6 +869,15 @@ static void forget_original_parent(struc
> LIST_HEAD(dead_children);
>
> write_lock_irq(&tasklist_lock);
> + list_for_each_entry_safe(p, n, &father->children_acct, sibling_acct) {
> + struct task_struct *t = p;
> + do {
> + t->acct_parent = t->acct_parent->acct_parent;
> + } while_each_thread(p, t);
> + list_move_tail(&p->sibling_acct,
> + &p->acct_parent->children_acct);
This is certainly wrong if there are other live threads in father's
thread-group.
Also, you need to change de_thread() if it changes the leader.
> list_for_each_entry_safe(p, n, &dead_children, sibling) {
> list_del_init(&p->sibling);
> + list_del_init(&p->sibling_acct);
This list_del() can race with ->acct_parent if it in turn exits and
does forget_original_parent() -> list_move_tail(sibling_acct).
Oleg.
next prev parent reply other threads:[~2010-10-06 15:31 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 [this message]
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
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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