linux-kernel - Re: [RFC/RFT PATCH] sched: automated per tty task groups

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Message-ID: <20101021105114.GA10216@Krystal>
Date:	Thu, 21 Oct 2010 06:51:14 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>
Subject: Re: [RFC/RFT PATCH] sched: automated per tty task groups

* Mike Galbraith (efault@....de) wrote:
[...]
> +static void
> +autogroup_attach_tty(struct task_struct *p, struct task_group **tg)
> +{
> +	struct tty_struct *tty = p->signal->tty;
> +
> +	if (!tty)
> +		return;
> +
> +	*tg = p->signal->tty->tg;
> +}
> +
> +static inline void
> +autogroup_check_attach(struct task_struct *p, struct task_group **tg)
> +{
> +	if (!sysctl_sched_autogroup_enabled || *tg != &root_task_group ||
> +			p->sched_class != &fair_sched_class)
> +		return;
> +
> +	rcu_read_lock();
> +
> +	autogroup_attach_tty(p, tg);
> +
> +	rcu_read_unlock();
> +}
> +

Hi Mike,

This per-tty task grouping approach looks very promising. I'll give it a spin
when I find the time. Meanwhile, a little question about locking here: how is
the read lock supposed to protect from p->signal (and p->signal->tty)
modifications ? What's the locking scheme here ? So maybe just simple
rcu_dereference are missing, or maybe the tsk->sighand->siglock might be
required. In all cases, I feel something is missing there. 

Thanks!

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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