linux-kernel - Re: wake_q memory ordering

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Message-ID: <20191011154623.zawmihahq6dria7u@linux-p48b>
Date:   Fri, 11 Oct 2019 08:46:23 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Manfred Spraul <manfred@...orfullife.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        1vier1@....de, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: wake_q memory ordering

On Fri, 11 Oct 2019, Manfred Spraul wrote:
>I don't know. The new documentation would not have answered my 
>question (is it ok to combine smp_mb__before_atomic() with 
>atomic_relaxed()?). And it copies content already present in 
>atomic_t.txt.

Well, the _relaxed (and release/acquire) extentions refer to a
_successful_ operation (LL/SC), and whether it has barriers on
each of the sides before and after. I thought you were mainly
worried about the failed CAS scenario, not the relaxed itself.

I don't know how this copies content from atomic_t.txt, at no
point does it talk about failed CAS.

>
>Thus: I would prefer if the first sentence of the paragraph is 
>replaced: The list of operations should end with "...", and it should 
>match what is in atomic_t.txt

I'll see about combining some of your changes in patch 5/5 of
your new series, but have to say I still prefer my documentation
change.

Thanks,
Davidlohr