linux-kernel - Re: [RFC][PATCH 11/18] sched: Add p->pi_lock to task_rq

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Date:	Wed, 5 Jan 2011 19:46:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>, 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 11/18] sched: Add p->pi_lock to task_rq_lock()

On 01/04, Peter Zijlstra wrote:
>
> This makes task_rq_lock() acquire both locks, and have
> __task_rq_lock() validate that p->pi_lock is held.

... and kills task_is_waking(), good ;)

So TASK_WAKING is only means "do not try to wakeup", this greatly
simplifies things.

One purely cosmetic nit,

> @@ -4902,8 +4898,7 @@ static int __sched_setscheduler(struct t
>
>  		check_class_changed(rq, p, prev_class, oldprio, running);
>  	}
> -	__task_rq_unlock(rq);
> -	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> +	task_rq_unlock(rq, p, &flags);

__sched_setscheduler() has a couple more instances of

	__task_rq_unlock(rq);
	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
	return EXXX;

above.

> @@ -5691,8 +5685,7 @@ int set_cpus_allowed_ptr(struct task_str
>  		return 0;
>  	}
>  out:
> -	__task_rq_unlock(rq);
> -	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> +	task_rq_unlock(rq, p, &flags);

the same.


Hmm, and normalize_rt_tasks(), it could just do task_rq_lock/task_rq_unlock.
And why it does read_lock_irqsave(tasklist), btw? _irqsave looks unneeded.

Oleg.

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