linux-kernel - Re: [PATCH -tip 2/3] sched/wake

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Date:	Wed, 16 Sep 2015 11:01:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH -tip 2/3] sched/wake_q: Relax to acquire semantics

On Tue, Sep 15, 2015 at 12:49:46PM -0700, Davidlohr Bueso wrote:
> On Tue, 15 Sep 2015, Peter Zijlstra wrote:
> 
> >>Secondly, the wake queues are not concurrent, they're in context, so I
> >>don't see ordering matter at all. The only reason its a cmpxchg() is
> >>because there is the (small) possibility of two contexts wanting to wake
> >>the same task, and we use task_struct storage for the queue.
> >
> >I don't think we need _any_ barriers here, unless we have concurrent
> >users of the wake queues (or want to allow any, do we?).
> 
> Exactly, the queues are not concurent and do not need barriers, but some of
> our callers do expect them.

Ah, that is what you were saying. In that case, I think we should remove
all our barriers and make them explicit in the callers where needed.
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