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tools/memory-model: Add litmus-test naming scheme

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This commit documents the scheme used to generate the names for the
litmus tests.

[ paulmck: Apply feedback from Andrea Parri and Will Deacon. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Link: http://lkml.kernel.org/r/20180926182920.27644-1-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Paul E. McKenney 2018-09-26 11:29:16 -07:00 committed by Ingo Molnar
parent 27df89689e
commit c4f790f244
1 changed files with 102 additions and 2 deletions
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tools/memory-model/litmus-tests/README
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@ -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 +153,101 @@ Z6.0+pooncerelease+poacquirerelease+fencembonceonce.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
The descriptors that describe connections between consecutive accesses
within the cycle through a given litmus test can be provided by the herd
tool (Rfi, Po, Fre, and so on) or by the linux-kernel.bell file (Once,
Release, Acquire, and so on).
To see the full list of descriptors, execute the following command:
$ diyone7 -bell linux-kernel.bell -show edges