linux-kernel - Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po

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Date:   Sat, 28 Jan 2023 23:14:17 +0100
From:   Andrea Parri <parri.andrea@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Jonas Oberhauser <jonas.oberhauser@...weicloud.com>,
        paulmck@...nel.org, will@...nel.org, peterz@...radead.org,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        j.alglave@....ac.uk, luc.maranget@...ia.fr, akiyks@...il.com,
        dlustig@...dia.com, joel@...lfernandes.org, urezki@...il.com,
        quic_neeraju@...cinc.com, frederic@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tools/memory-model: Make ppo a subrelation of po

> Evidently the plain-coherence check rules out x=1 at the 
> end, because when I relax that check, x=1 becomes a possible result.  
> Furthermore, the graphical output confirms that this execution has a 
> ww-incoh edge from Wx=2 to Wx=1.  But there is no ww-vis edge from Wx=1 
> to Wx=2!  How can this be possible?  It seems like a bug in herd7.

By default, herd7 performs some edges removal when generating the
graphical outputs.  The option -showraw can be useful to increase
the "verbosity", for example,

  [with "exists (x=2)", output in /tmp/T.dot]
  $ herd7 -conf linux-kernel.cfg T.litmus -show prop -o /tmp -skipchecks plain-coherence -doshow ww-vis -showraw ww-vis


> Furthermore, the execution with x=2 at the end doesn't have either a 
> ww-vis or a ww-nonrace edge betwen Wx=1 and Wx=2.  So why isn't there a 
> ww-race edge?

And similarly

  [with "exists (x=2)"]
  $ herd7 -conf linux-kernel.cfg T.litmus -show prop -o /tmp -doshow ww-vis,ww-nonrace -showraw ww-vis,ww-nonrace

  Andrea