linux-kernel - Re: [PATCH] tools/memory-model: Weaken ctrl dependency definition in explanation.txt

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Message-Id: <2FD673C3-F8FA-428C-B8B1-4DBC71AFDF0C@in.tum.de>
Date:   Fri, 2 Sep 2022 22:53:26 +0200
From:   Paul Heidekrüger <Paul.Heidekrueger@...tum.de>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Marco Elver <elver@...gle.com>,
        Charalampos Mainas <charalampos.mainas@...il.com>,
        Pramod Bhatotia <pramod.bhatotia@...tum.de>,
        Soham Chakraborty <s.s.chakraborty@...elft.nl>,
        Martin Fink <martin.fink@...tum.de>
Subject: Re: [PATCH] tools/memory-model: Weaken ctrl dependency definition in
 explanation.txt

On 2. Sep 2022, at 16:18, Alan Stern <stern@...land.harvard.edu> wrote:

> On Fri, Sep 02, 2022 at 10:40:34AM +0200, Paul Heidekrüger wrote:
>> On 31. Aug 2022, at 19:38, Alan Stern <stern@...land.harvard.edu> wrote:
>>>>> Finally, a read event X and another memory access event Y are linked by a
>>>>> control dependency if Y syntactically lies within an arm of an if
>>>>> statement and X affects the evaluation of the if condition via a data or
>>>>> address dependency.  Similarly for switch statements.
>>>> 
>>>> What do you think?
>>> 
>>> I like the second one.  How about combining the last two sentences?  
>>> 
>>> 	... via a data or address dependency (or similarly for a switch 
>>> 	statement).
>> 
>> Yes, sounds good!
>> 
>>> Now I suppose someone will pipe up and ask about the conditional 
>>> expressions in "for", "while" and "do" statements...  :-)
>> 
>> Happy to have obliged :-)
>> https://lore.kernel.org/all/20F4C097-24B4-416B-95EE-AC11F5952B44@in.tum.de/
>> 
>> Do you think the text should explicitly address control dependencies in the
>> context of loops as well? If yes, would it be a separate patch, or would it
>> make sense to combine it with this one?
> 
> Anything else should be a separate patch.
> 
> For the time being, I'm happy not to worry about loops.  In the end
> we'll probably have to describe them as though they were unrolled,
> with all the complications that entails.

OK, sounds good!

Since there aren't any other immediate objections, I'll go ahead an resubmit
a v3 version of the patch with all the changes we discussed then.

Many thanks,
Paul
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