linux-kernel - Re: [RFC][PATCH 05/18] sched: Provide p->on

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Message-ID: <4D435B10.3050207@am.sony.com>
Date:	Fri, 28 Jan 2011 16:10:56 -0800
From:	Frank Rowand <frank.rowand@...sony.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Chris Mason <chris.mason@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 05/18] sched: Provide p->on_rq

On 01/04/11 06:59, Peter Zijlstra wrote:
Provide a generic p->on_rq because the p->se.on_rq semantics are
> unfavourable for lockless wakeups but needed for sched_fair.
>
> In particular, p->on_rq is only cleared when we actually dequeue the
> task in schedule() and not on any random dequeue as done by things
> like __migrate_task() and __sched_setscheduler().
>
> This also allows us to remove p->se usage from !sched_fair code.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  include/linux/sched.h   |    1 +
>  kernel/sched.c          |   36 ++++++++++++++++++------------------
>  kernel/sched_debug.c    |    2 +-
>  kernel/sched_rt.c       |   10 +++++-----
>  kernel/sched_stoptask.c |    2 +-
>  5 files changed, 26 insertions(+), 25 deletions(-)

> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c


> @@ -2571,18 +2570,20 @@ int wake_up_state(struct task_struct *p,
>   */
>  static void __sched_fork(struct task_struct *p)
>  {
> +     p->on_rq                                = 0;

Nitpick: column alignment of "= 0" ^^^^.


> +
> +     p->se.on_rq                     = 0;
>       p->se.exec_start                = 0;
>       p->se.sum_exec_runtime          = 0;
>       p->se.prev_sum_exec_runtime     = 0;
>       p->se.nr_migrations             = 0;
> +     INIT_LIST_HEAD(&p->se.group_node);
>
>  #ifdef CONFIG_SCHEDSTATS
>       memset(&p->se.statistics, 0, sizeof(p->se.statistics));
>  #endif
>
>       INIT_LIST_HEAD(&p->rt.run_list);
> -     p->se.on_rq = 0;
> -     INIT_LIST_HEAD(&p->se.group_node);
>
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
>       INIT_HLIST_HEAD(&p->preempt_notifiers);
>


-Frank

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