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Subject: Re: Section 9.5: Nobody expects the Spanish Acquisition!
References: <CAJbg=FWZG2EicBGKBbVzYnhH7oT3FqkwY738pmra9G9riGssVQ@mail.gmail.com>
From: Akira Yokosawa <akiyks@gmail.com>
Message-ID: <b2851e07-d804-eff9-cb48-c636a159f868@gmail.com>
Date: Wed, 22 Dec 2021 17:21:27 +0900
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To: Elad Lahav <e2lahav@gmail.com>
Cc: perfbook@vger.kernel.org, "Paul E. McKenney" <paulmck@kernel.org>
List-ID: <perfbook.vger.kernel.org>

(+explicit Cc: Paul)

Hi Elad,

On Tue, 21 Dec 2021 10:20:52 -0500, Elad Lahav wrote:
> Hi Paul,
> 
> As promised, I have a potentially more interesting comment regarding
> Section 9.5. Throughout this section, from the very first example, the
> writer uses release semantics, but the readers are not obligated to
> use acquire semantics, at least on sensible architectures (with
> apologies to employees of HP nee Compaq nee Digital).

  ;-)

> 
> If I understand correctly, these relaxed semantics are the result of
> an address dependency, with the data protected by the RCU critical
> section residing in a structure whose address is stored by the pointer
> dereferenced by a reader. The reader cannot consider any data outside
> of this structure as protected by the critical section. This is a
> critical point without which the examples won't work reliably.

I think this is mostly covered in Section 9.5.2.1 "Publish-Subscribe
Mechanism" and Figure 9.10 "Publication/Subscription Constraints".

> 
> Am I missing something? If not, I think that this point should be
> emphasized early on, with a link to Section 15.2.3.

There is such a reference in Section 9.5.2.1 just below Quick Quiz
9.28.  You mean you find this too late?

        Thanks, Akira

BTW, I couldn't figure out what you meant by "the Spanish
Acquisition"...

> 
> --Elad
>