[PATCH memory-model 1/5] tools/memory-model: Add litmus-test naming scheme

From: Paul E. McKenney
Date: Wed Sep 26 2018 - 14:31:22 EST

From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

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

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
[ paulmck: Apply feedback from Andrea Parri and Will Deacon. ]
Acked-by: Will Deacon <will.deacon@xxxxxxx>
tools/memory-model/litmus-tests/README | 104 ++++++++++++++++++++++++-
1 file changed, 102 insertions(+), 2 deletions(-)

diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
index 4581ec2d3c57..5ee08f129094 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:

Test of read-read coherence, that is, whether or not two
@@ -36,7 +38,7 @@ IRIW+poonceonces+OnceOnce.litmus
Tests whether the ordering provided by a lock-protected S
litmus test is visible to an external process whose accesses are
- separated by smp_mb(). This addition of an external process to
+ separated by smp_mb(). This addition of an external process to
S is otherwise known as ISA2.

@@ -151,3 +153,101 @@ Z6.0+pooncerelease+poacquirerelease+fencembonceonce.litmus
A great many more litmus tests are available here:

+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:
+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