linux-kernel - Re: [RFC][PATCH 02/11] sched: Create preempt

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Message-ID: <20150929140946.GI3816@twins.programming.kicks-ass.net>
Date:	Tue, 29 Sep 2015 16:09:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, fweisbec@...il.com, oleg@...hat.com,
	umgwanakikbuti@...il.com, rostedt@...dmis.org
Subject: Re: [RFC][PATCH 02/11] sched: Create preempt_count invariant

On Tue, Sep 29, 2015 at 03:11:56PM +0200, Thomas Gleixner wrote:
> On Tue, 29 Sep 2015, Peter Zijlstra wrote:
> > +	/*
> > +	 * Still have preempt_count() == 2, from:
> > +	 *
> > +	 *	schedule()
> > +	 *	  preempt_disable();			// 1
> > +	 *	  __schedule()
> > +	 *	    raw_spin_lock_irq(&rq->lock)	// 2
> > +	 */
> > +	rq = finish_task_switch(prev); /* drops rq->lock, preempt_count() == 1 */
> >  	balance_callback(rq);
> > -	preempt_enable();
> > +	preempt_enable(); /* preempt_count() == 0 */
> 
> Bah. I so hate tail comments. What's wrong with
> 
> +	 /* preempt_count() ==> 0 */
> 	preempt_enable();
> 
> Hmm?

I find the tail comments more readable in this case; clearly I don't
share your hatred :-). But I can change them if you insist.

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