linux-kernel - Re: [PATCH] tools/memory-model: Document herd7 (internal) representation

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Date: Mon, 27 May 2024 15:28:00 +0200
From: Andrea Parri <parri.andrea@...il.com>
To: Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>
Cc: stern@...land.harvard.edu, will@...nel.org, peterz@...radead.org,
	boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
	j.alglave@....ac.uk, luc.maranget@...ia.fr, paulmck@...nel.org,
	akiyks@...il.com, dlustig@...dia.com, joel@...lfernandes.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	jonas.oberhauser@...weicloud.com
Subject: Re: [PATCH] tools/memory-model: Document herd7 (internal)
 representation

> > +    |                smp_store_mb | W[once] ->po F[mb]                        |
> 
> I expect this one to be hard-coded in herd7 source code, but I cannot find
> it. Can you give me a pointer?

smp_store_mb() is currently mapped to { __store{once}(X,V); __fence{mb}; } in
the .def file, so it's semantically equivalent to "WRITE_ONCE(); smp_mb();".

> What about spin_unlock?

spin_unlock() is listed among the non-RMW ops/macros in the current table: it
is represented by a single UL or "Unlock" event (a special type of Store event
with (some special) Release semantics).

> I found the extra spaces in the failure case very hard to read. Any
> particular reason why you went with this format?

The extra spaces were simply to convey something like "belong to the previous
row/entry", but I'm open to remove them or other suggestions if preferred.

  Andrea