This commit documents the scheme used to generate the names for the litmus tests. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- README | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 135 insertions(+), 1 deletion(-) diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README index 00140aaf58b7..b81f51054cd3 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 +153,135 @@ 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 finite-length 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 | classify7 -bell linux-kernel.bell -diyone | 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: + +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 rrote 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. Example: ??? + Comparison to PosWR??? +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: ???
