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Date:   Tue, 29 May 2018 05:19:41 -0700
From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     Andrea Parri <andrea.parri@amarulasolutions.com>
Cc:     linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        stern@rowland.harvard.edu, will.deacon@arm.com,
        peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com,
        dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr,
        akiyks@gmail.com, mingo@kernel.org
Subject: Re: [PATCH RFC tools/memory-model] Add litmus-test naming scheme
Reply-To: paulmck@linux.vnet.ibm.com
References: <20180525191020.GA5914@linux.vnet.ibm.com>
 <20180528112010.GA8801@andrea>
 <20180528214838.GZ3803@linux.vnet.ibm.com>
 <20180529093350.GA5803@andrea>
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On Tue, May 29, 2018 at 11:33:50AM +0200, Andrea Parri wrote:
> [...]
> 
> > > We used to distinguigh between the test name and the test filename; we
> > > currently have only one test whose name ends with .litmus:
> > > 
> > >   ISA2+pooncelock+pooncelock+pombonce.litmus
> > > 
> > > (that I missed until now...).
> > 
> > I queued a commit to fix this with your Reported-by, good catch!
> 
> Thanks for the fix.
> 
> > > I also notice that, with the current version, the above command can be
> > > simplified to:
> > > 
> > >   $ norm7 -bell linux-kernel.bell Rfi Once PodRR Once Fre Once Rfi Once PodRR Once Fre Once | sed -e 's/:.*//g'
> > 
> > Dropping the "classify7" command, correct?
> 
> Right, thanks.  Ah, maybe we should strive to meet the 80-chars bound
> by splitting the command with "\"?

We could, but combined with your later request for indentation, we end
up with something like this:

	$ norm7 -bell linux-kernel.bell \
		Rfi Once PodRR Once Fre Once Rfi Once PodRR Once Fre Once | \
	  sed -e 's/:.*//g'
	SB+rfionceonce-poonceonces

In the immortal words of MSDOS, are you sure?  ;-)

> > > Maybe expand to recall that we're referring to a particular cycle (the
> > > cycle referred to in the previous section)? (the term 'consecutive' is
> > > overloaded ;-)
> > 
> > Well, it is an English word, so overloading is the common case.  ;-)
> > 
> > How about this?
> 
> Looks better, thanks.
> 
> > > I'm not sure if it is worth commenting on this, but compare, e.g., the
> > > 'exists' clauses of the following two tests (thinking at 'coherence'):
> > > 
> > > $ diyone7 -arch LISA PosWR PodRR Fre PosWR PodRR Fre
> > > LISA A
> > > "PosWR PodRR Fre PosWR PodRR Fre"
> > > Generator=diyone7 (version 7.49+02(dev))
> > > Prefetch=0:x=F,0:y=T,1:y=F,1:x=T
> > > Com=Fr Fr
> > > Orig=PosWR PodRR Fre PosWR PodRR Fre
> > > {
> > > }
> > >  P0       | P1       ;
> > >  w[] x 1  | w[] y 1  ;
> > >  r[] r0 x | r[] r0 y ;
> > >  r[] r1 y | r[] r1 x ;
> > > exists
> > > (0:r1=0 /\ 1:r1=0)
> > > 
> > > $ diyone7 -arch LISA Rfi PodRR Fre Rfi PodRR Fre
> > > LISA A
> > > "Rfi PodRR Fre Rfi PodRR Fre"
> > > Generator=diyone7 (version 7.49+02(dev))
> > > Prefetch=0:x=F,0:y=T,1:y=F,1:x=T
> > > Com=Fr Fr
> > > Orig=Rfi PodRR Fre Rfi PodRR Fre
> > > {
> > > }
> > >  P0       | P1       ;
> > >  w[] x 1  | w[] y 1  ;
> > >  r[] r0 x | r[] r0 y ;
> > >  r[] r1 y | r[] r1 x ;
> > > exists
> > > (0:r0=1 /\ 0:r1=0 /\ 1:r0=1 /\ 1:r1=0)
> > 
> > How about this?
> > 
> > fi: Read-from internal.  The current process wrote a variable and then
> > 	immediately read the value back from it.  For the purposes of
> > 	naming, Rfi acts identically to PosWR.
> 
> Well, "Rfi" produces "rfi" while "PosWR" produces "pos" for a name...

Right you are!  How about this, then?

Rfi: Read-from internal.  The current process wrote a variable and then
        immediately read the value back from it.  For the purposes of
        litmus-test code generation, Rfi acts identically to PosWR.
        However, they differ for purposes of naming, and they also result
        in different "exists" clauses.
	Example:  ???

> > However, there are subtle
> > 	but very real differences between them in other contexts.
> 
> I think that you're fascinated by the evocative power of English words. ;-)

If you didn't know better, you might even think that I was a native
English speaker!  ;-)

> > > The list of descriptors is incomplete; the command:
> > > 
> > >   $ diyone7 -bell linux-kernel.bell -show edges
> > > 
> > > shows other descriptors (including fences and dependencies).  We might
> > > want to list this command; searching the commit history, I found:
> > > 
> > >    3c24730ef6c662 ("gen: Add a new command line option -show (edges|fences|annotations) that list various categories of candidate relaxations.")
> > 
> > Yow!!!
> > 
> >  CtrldR CtrldW CtrlsR CtrlsW DpAddrdR DpAddrdW DpAddrsR DpAddrsW DpCtrldR DpCtrldW DpCtrlsR DpCtrlsW DpDatadW DpDatasW Dpd* DpdR DpdW Dps* DpsR DpsW FenceAfter-atomic FenceAfter-atomicd** FenceAfter-atomicd*R FenceAfter-atomicd*W FenceAfter-atomicdR* FenceAfter-atomicdRR FenceAfter-atomicdRW FenceAfter-atomicdW* FenceAfter-atomicdWR FenceAfter-atomicdWW FenceAfter-atomics** FenceAfter-atomics*R FenceAfter-atomics*W FenceAfter-atomicsR* FenceAfter-atomicsRR FenceAfter-atomicsRW FenceAfter-atomicsW* FenceAfter-atomicsWR FenceAfter-atomicsWW FenceAfter-spinlock FenceAfter-spinlockd** FenceAfter-spinlockd*R FenceAfter-spinlockd*W FenceAfter-spinlockdR* FenceAfter-spinlockdRR FenceAfter-spinlockdRW FenceAfter-spinlockdW* FenceAfter-spinlockdWR FenceAfter-spinlockdWW FenceAfter-spinlocks** FenceAfter-spinlocks*R FenceAfter-spinlocks*W FenceAfter-spinlocksR* FenceAfter-spinlocksRR FenceAfter-spinlocksRW FenceAfter-spinlocksW* FenceAfter-spinlocksWR FenceAfter-spinlocksWW FenceBefore-atomic FenceBefore-atomicd** FenceBefore-atomicd*R FenceBefore-atomicd*W FenceBefore-atomicdR* FenceBefore-atomicdRR FenceBefore-atomicdRW FenceBefore-atomicdW* FenceBefore-atomicdWR FenceBefore-atomicdWW FenceBefore-atomics** FenceBefore-atomics*R FenceBefore-atomics*W FenceBefore-atomicsR* FenceBefore-atomicsRR FenceBefore-atomicsRW FenceBefore-atomicsW* FenceBefore-atomicsWR FenceBefore-atomicsWW FenceMb FenceMbd** FenceMbd*R FenceMbd*W FenceMbdR* FenceMbdRR FenceMbdRW FenceMbdW* FenceMbdWR FenceMbdWW FenceMbs** FenceMbs*R FenceMbs*W FenceMbsR* FenceMbsRR FenceMbsRW FenceMbsW* FenceMbsWR FenceMbsWW FenceRcu-lock FenceRcu-lockd** FenceRcu-lockd*R FenceRcu-lockd*W FenceRcu-lockdR* FenceRcu-lockdRR FenceRcu-lockdRW FenceRcu-lockdW* FenceRcu-lockdWR FenceRcu-lockdWW FenceRcu-locks** FenceRcu-locks*R FenceRcu-locks*W FenceRcu-locksR* FenceRcu-locksRR FenceRcu-locksRW FenceRcu-locksW* FenceRcu-locksWR FenceRcu-locksWW FenceRcu-unlock FenceRcu-unlockd** FenceRcu-unlockd*R FenceRcu-unlockd*W FenceRcu-unlockdR* FenceRcu-unlockdRR FenceRcu-unlockdRW FenceRcu-unlockdW* FenceRcu-unlockdWR FenceRcu-unlockdWW FenceRcu-unlocks** FenceRcu-unlocks*R FenceRcu-unlocks*W FenceRcu-unlocksR* FenceRcu-unlocksRR FenceRcu-unlocksRW FenceRcu-unlocksW* FenceRcu-unlocksWR FenceRcu-unlocksWW FenceRmb FenceRmbd** FenceRmbd*R FenceRmbd*W FenceRmbdR* FenceRmbdRR FenceRmbdRW FenceRmbdW* FenceRmbdWR FenceRmbdWW FenceRmbs** FenceRmbs*R FenceRmbs*W FenceRmbsR* FenceRmbsRR FenceRmbsRW FenceRmbsW* FenceRmbsWR FenceRmbsWW FenceSync-rcu FenceSync-rcud** FenceSync-rcud*R FenceSync-rcud*W FenceSync-rcudR* FenceSync-rcudRR FenceSync-rcudRW FenceSync-rcudW* FenceSync-rcudWR FenceSync-rcudWW FenceSync-rcus** FenceSync-rcus*R FenceSync-rcus*W FenceSync-rcusR* FenceSync-rcusRR FenceSync-rcusRW FenceSync-rcusW* FenceSync-rcusWR FenceSync-rcusWW FenceWmb FenceWmbd** FenceWmbd*R FenceWmbd*W FenceWmbdR* FenceWmbdRR FenceWmbdRW FenceWmbdW* FenceWmbdWR FenceWmbdWW FenceWmbs** FenceWmbs*R FenceWmbs*W FenceWmbsR* FenceWmbsRR FenceWmbsRW FenceWmbsW* FenceWmbsWR FenceWmbsWW Fenced** Fenced*R Fenced*W FencedR* FencedRR FencedRW FencedW* FencedWR FencedWW Fences** Fences*R Fences*W FencesR* FencesRR FencesRW FencesW* FencesWR FencesWW FrBack FrLeave Fre Fri Hat Na Pod** Pod*R Pod*W PodR* PodRR PodRW PodW* PodWR PodWW Pos** Pos*R Pos*W PosR* PosRR PosRW PosW* PosWR PosWW R Read RfBack RfLeave Rfe Rfi Rmw W Write WsBack WsLeave Wse Wsi
> > 
> > I added the following at the end:
> > 
> > Please note that the above is a partial list.  To see the full list of
> > descriptors, execute the following command:
> > 
> > $ diyone7 -bell linux-kernel.bell -show edges
> 
> Thanks.  One more nit: I'd indent this and the above "norm7" commands as
> we do in our "main" README.

Done!

> > > I also notice that our current names for tests with fences (and cycle)
> > > deviate from the corresponding 'norm7' results; e.g.,
> > > 
> > >   $ norm7 -bell linux-kernel.bell FenceWmbdWW Once Rfe Once FenceRmbdRR Once Fre Once | sed -e 's/:.*//g'
> > >   MP+fencewmbonceonce+fencermbonceonce
> > > 
> > > while we use 'MP+wmbonceonce+rmbonceonce' (that is, we omit the 'fence'
> > > prefixes).
> > 
> > Would you be willing to send me a patch fixing them up?
> 
> Yes, I'll work this out.

Thanks in advance!

							Thanx, Paul

>   Andrea
> 
> 
> > 
> > Please see below for updated patch.
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 04a897a8e202e8d79dd47910321f0e8efb081854
> > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Date:   Fri May 25 12:02:53 2018 -0700
> > 
> >     EXP tools/memory-model: Add litmus-test naming scheme
> >     
> >     This commit documents the scheme used to generate the names for the
> >     litmus tests.
> >     
> >     Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> >     [ paulmck: Apply feedback from Andrea Parri. ]
> > 
> > diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
> > index 00140aaf58b7..9c0ea65c5362 100644
> > --- a/tools/memory-model/litmus-tests/README
> > +++ b/tools/memory-model/litmus-tests/README
> > @@ -1,4 +1,6 @@
> > -This directory contains the following litmus tests:
> > +============
> > +LITMUS TESTS
> > +============
> >  
> >  CoRR+poonceonce+Once.litmus
> >  	Test of read-read coherence, that is, whether or not two
> > @@ -151,3 +153,143 @@ Z6.0+pooncerelease+poacquirerelease+mbonceonce.litmus
> >  A great many more litmus tests are available here:
> >  
> >  	https://github.com/paulmckrcu/litmus
> > +
> > +==================
> > +LITMUS TEST NAMING
> > +==================
> > +
> > +Litmus tests are usually named based on their contents, which means that
> > +looking at the name tells you what the litmus test does.  The naming
> > +scheme covers litmus tests having a single cycle that passes through
> > +each process exactly once, so litmus tests not fitting this description
> > +are named on an ad-hoc basis.
> > +
> > +The structure of a litmus-test name is the litmus-test class, a plus
> > +sign ("+"), and one string for each process, separated by plus signs.
> > +The end of the name is ".litmus".
> > +
> > +The litmus-test classes may be found in the infamous test6.pdf:
> > +https://www.cl.cam.ac.uk/~pes20/ppc-supplemental/test6.pdf
> > +Each class defines the pattern of accesses and of the variables accessed.
> > +For example, if the one process writes to a pair of variables, and
> > +the other process reads from these same variables, the corresponding
> > +litmus-test class is "MP" (message passing), which may be found on the
> > +left-hand end of the second row of tests on page one of test6.pdf.
> > +
> > +The strings used to identify the actions carried out by each process are
> > +complex due to a desire to have short(er) names.  Thus, there is a tool to
> > +generate these strings from a given litmus test's actions.  For example,
> > +consider the processes from SB+rfionceonce-poonceonces.litmus:
> > +
> > +	P0(int *x, int *y)
> > +	{
> > +		int r1;
> > +		int r2;
> > +
> > +		WRITE_ONCE(*x, 1);
> > +		r1 = READ_ONCE(*x);
> > +		r2 = READ_ONCE(*y);
> > +	}
> > +
> > +	P1(int *x, int *y)
> > +	{
> > +		int r3;
> > +		int r4;
> > +
> > +		WRITE_ONCE(*y, 1);
> > +		r3 = READ_ONCE(*y);
> > +		r4 = READ_ONCE(*x);
> > +	}
> > +
> > +The next step is to construct a space-separated list of descriptors,
> > +interleaving descriptions of the relation between a pair of consecutive
> > +accesses with descriptions of the second access in the pair.
> > +
> > +P0()'s WRITE_ONCE() is read by its first READ_ONCE(), which is a
> > +reads-from link (rf) and internal to the P0() process.  This is
> > +"rfi", which is an abbreviation for "reads-from internal".  Because
> > +some of the tools string these abbreviations together with space
> > +characters separating processes, the first character is capitalized,
> > +resulting in "Rfi".
> > +
> > +P0()'s second access is a READ_ONCE(), as opposed to (for example)
> > +smp_load_acquire(), so next is "Once".  Thus far, we have "Rfi Once".
> > +
> > +P0()'s third access is also a READ_ONCE(), but to y rather than x.
> > +This is related to P0()'s second access by program order ("po"),
> > +to a different variable ("d"), and both accesses are reads ("RR").
> > +The resulting descriptor is "PodRR".  Because P0()'s third access is
> > +READ_ONCE(), we add another "Once" descriptor.
> > +
> > +A from-read ("fre") relation links P0()'s third to P1()'s first
> > +access, and the resulting descriptor is "Fre".  P1()'s first access is
> > +WRITE_ONCE(), which as before gives the descriptor "Once".  The string
> > +thus far is thus "Rfi Once PodRR Once Fre Once".
> > +
> > +The remainder of P1() is similar to P0(), which means we add
> > +"Rfi Once PodRR Once".  Another fre links P1()'s last access to
> > +P0()'s first access, which is WRITE_ONCE(), so we add "Fre Once".
> > +The full string is thus:
> > +
> > +	Rfi Once PodRR Once Fre Once Rfi Once PodRR Once Fre Once
> > +
> > +This string can be given to the "norm7" and "classify7" tools to
> > +produce the name:
> > +
> > +$ norm7 -bell linux-kernel.bell Rfi Once PodRR Once Fre Once Rfi Once PodRR Once Fre Once | sed -e 's/:.*//g'
> > +SB+rfionceonce-poonceonces
> > +
> > +Adding the ".litmus" suffix: SB+rfionceonce-poonceonces.litmus
> > +
> > +
> > +=======================
> > +LITMUS TEST DESCRIPTORS
> > +=======================
> > +
> > +These descriptors cover connections between consecutive accesses within
> > +the cycle through a given litmus test:
> > +
> > +Fre: From-read external.  The current process wrote a variable that
> > +	the previous process read.  Example: The SB (store buffering) test.
> > +Fri: From-read internal.  This process read a variable and then
> > +	immediately wrote to it.  Example: ???
> > +PodRR: Program-order different variable, read followed by read.
> > +	This process read a variable and again read a different variable.
> > +	Example: The read-side process in the MP (message-passing) test.
> > +PodRW: Program-order different variable, read followed by write.
> > +	This process read a variable and then wrote a different variable.
> > +	Example: The LB (load buffering) test.
> > +PodWR: Program-order different variable, write followed by read.
> > +	This process wrote a variable and then read a different variable.
> > +	Example: The SB (store buffering) test.
> > +PodWW: Program-order different variable, write followed by write.
> > +	This process wrote a variable and again wrote a different variable.
> > +	Example: The write-side process in the MP (message-passing) test.
> > +PosRR: Program-order same variable, read followed by read.
> > +	This process read a variable and again read that same variable.
> > +	Example: ???
> > +PosRW: Program-order same variable, read followed by write.
> > +	This process read a variable and then wrote that same variable.
> > +	Example: ???
> > +PosWR: Program-order same variable, write followed by read.
> > +	This process wrote a variable and then read that same variable.
> > +	Example: ???
> > +PosWW: Program-order same variable, write followed by write.
> > +	This process wrote a variable and again wrote that same variable.
> > +	Example: ???
> > +Rfe: Read-from external.  The current process read a variable written
> > +	by the previous process.  Example: The MP (message passing) test.
> > +Rfi: Read-from internal.  The current process wrote a variable and then
> > +	immediately read the value back from it.  For the purposes of
> > +	naming, Rfi acts identically to PosWR.	However, there are subtle
> > +	but very real differences between them in other contexts.
> > +	Example:  ???
> > +Wse: Write same external.  The current process wrote to a variable that
> > +	was also written to by the previous process.  Example:  ???
> > +Wsi: Write same internal.  The current process wrote to a variable and
> > +	then immediately wrote to it again.  Example:  ???
> > +
> > +Please note that the above is a partial list.  To see the full list of
> > +descriptors, execute the following command:
> > +
> > +$ diyone7 -bell linux-kernel.bell -show edges
> > 
>