linux-kernel - Re: [PATCH memory-model] docs: memory-barriers: Add note on compiler transformation and address deps

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Message-ID: <591279ff-3316-d64b-8b25-6baefcecaad1@huaweicloud.com>
Date:   Sat, 21 Oct 2023 15:36:21 +0200
From:   Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
To:     paulmck@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
        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>,
        Akira Yokosawa <akiyks@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH memory-model] docs: memory-barriers: Add note on compiler
 transformation and address deps


Am 10/20/2023 um 8:13 PM schrieb Paul E. McKenney:
> On Fri, Oct 20, 2023 at 06:00:19PM +0200, Jonas Oberhauser wrote:
>> Am 10/20/2023 um 3:57 PM schrieb Paul E. McKenney:
>>> On Fri, Oct 20, 2023 at 11:29:24AM +0200, Jonas Oberhauser wrote:
>>>> Am 10/19/2023 um 6:39 PM schrieb Paul E. McKenney:
>>>>> On Wed, Oct 18, 2023 at 12:11:58PM +0200, Jonas Oberhauser wrote:
>>>>>> Hi Paul,
>>>>>> [...]
>>>>> The compiler is forbidden from inventing pointer comparisons.
>>>> TIL :) Btw, do you remember a discussion where this is clarified? A quick
>>>> search didn't turn up anything.
>>> This was a verbal discussion with Richard Smith at the 2020 C++ Standards
>>> Committee meeting in Prague.  I honestly do not know what standardese
>>> supports this.
>> Richard Smith
>> Then this e-mail thread shall be my evidence for future discussion.
> I am sure that Richard will be delighted, especially given that he
> did not seem at all happy with this don't-invent-pointer-comparisons
> rule.  ;-)


Neither am I :D
He can voice his delightenment or lack thereof to me if we ever happen 
to meet in person.


>> I think this tiny rewrite makes it much more clear. Specifically it tells *why* the text is historical (and why we maybe don't need to read it anymore).
> Good point!  I reworked this a bit and added it to both HISTORICAL
> sections, with your Suggested-by.


The new version looks good to me!


>>>>> The longer-term direction, perhaps a few years from now, is for the
>>>>> first section to simply reference rcu_dereference.rst and for the second
>>>>> section to be removed completely.
>>>> Sounds good to me, but that doesn't mean we need to compromise the
>>>> readability in the interim :)
>>> Some compromise is needed for people that read the document some time
>>> back and are looking for something specific.
>> Yes. But the compromise should be "there's a blob of text other people don't
>> need to read", not "there's a blob of text that will leave other people
>> confused".
> Fair enough in general, but I cannot promise to never confuse people.
> This is after all memory ordering.  And different people will be confused
> by different things.


You can say that twice. In fact I suspect this is not the first time you 
say that :))

   jonas