linux-kernel - Re: [PATCH v2] ipc/msg: Implement lockless pipelined wakeups

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Message-ID: <20151104173217.GA15994@linux-uzut.site>
Date:	Wed, 4 Nov 2015 09:32:17 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org, George Spelvin <linux@...izon.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Manfred Spraul <manfred@...orfullife.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] ipc/msg: Implement lockless pipelined wakeups

On Wed, 04 Nov 2015, Peter Zijlstra wrote:

>On Tue, Nov 03, 2015 at 04:03:29PM +0100, Sebastian Andrzej Siewior wrote:
>
>> -	struct msg_msg		*volatile r_msg;
>> +	struct msg_msg		*r_msg;
>
>> +				wake_q_add(wake_q, msr->r_tsk);
>>  				msr->r_msg = msg;
>> +				/*
>> +				 * Rely on the implicit cmpxchg barrier from
>> +				 * wake_q_add such that we can ensure that
>
>Davidlohr, didn't you want to make that cmpxchg_relaxed() or
>cmpxchg_release() ?

Right, I had forgotten about that. iirc we ended up deciding to fully
relax the cmpxchg and update the callers instead.
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