linux-kernel - Re: [BUG] scheduler: first timeslice of the exiting thread

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Message-ID: <20070409110333.GA253@tv-sign.ru>
Date:	Mon, 9 Apr 2007 15:03:33 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org
Subject: Re: [BUG] scheduler: first timeslice of the exiting thread

On 04/09, Oleg Nesterov wrote:
>
> Satoru Takeuchi wrote:
> >
> >   a) On sched_fork, the creator share its timeslice with new process.
> >   b) On sched_exit, if the exiting process didn't exhaust its first
> >      timeslice yet, it gives its timeslice to the parent.
> >
> > It has no problem on the process model since the creator is the parent.
> > However, on the thread model, the creator is not the parent, it is same
> > as the creator's parent. Hence, on this kind of program, the creator
> > can't retrieve shared timeslice and exausts its timeslice at a rate of
> > knots. In addition, somehow, the parent (typically shell?) gets extra
> > timeslice.
> 
> Yes, this is an old oddity.

Perhaps

	void sched_exit(struct task_struct *p)
	{
		task_t *t, *did_fork = p->parent;

		if (!thread_group_leader(p))
			list_for_each_entry(t, p->thread_group)
				if (!t->exit_state) {
					did_fork = t;
					break;
				}

		... give time_slice to did_fork ..
	}

may improve things a little bit, because the rest of time_slice doesn't leak
off the thread group.

However this is not very nice and we have the same problem with CLONE_PARENT.

Oleg.

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