litmus7 (http://diy.inria.fr/doc/litmus.html) is a tool that takes as an input a litmus test specification and generates a program that can execute on hardware. Using kvm-unit-tests, litmus7 can generate tests that run on KVM. This change adds some documentation to introduce this functionality along with a basic example of how to build and run such tests. Signed-off-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx> --- README.litmus7.md | 125 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 125 insertions(+) create mode 100644 README.litmus7.md diff --git a/README.litmus7.md b/README.litmus7.md new file mode 100644 index 0000000..4653488 --- /dev/null +++ b/README.litmus7.md @@ -0,0 +1,125 @@ +# Memory model litmus tests as kvm-unit-tests + +In this guide, we explain how to use kvm-unit-tests in combination +with litmus7 to generate and run litmus tests as tiny operating +systems. + +## Background + +### Memory model litmus tests + +A litmus test is a small program designed to exercise a certain +behavior. Traditionally, litmus tests have been used to demonstrate +and exercise the memory model of parallel computing systems. Litmus +tests are often described in assembly or pseudo-assembly code and +require tools like [litmus7](http://diy.inria.fr/doc/litmus.html) to +genererate executable programs that we can then run on real hardware. + +### Why kvm-unit-tests + +litmus7 uses kvm-unit-tests to encapsulate a litmus tests and generate +executables in the form of tiny operating systems. Inside these tiny +operating systems, the litmus tests can control parameters of the +execution that a user space application cannot. For example, control +virtual address translation and handle exceptions. + +## Building and running litmus kvm-unit-tests + +litmus7 is a tool that given a litmus test will generate C source +code. The generated C source code is compiled and linked with +kvm-unit-tests to generate the binary. + +## Prerequisites + +litmus7 is part of the herdtools7 toolsuite. See +https://github.com/herd/herdtools7/blob/master/INSTALL.md for +instructions of how to build and install herdtools7 from source. + +In addition to herdtools7, this guide assumes that you have a copy of +kvm-unit-tests and you have already configured and built the included +tests. + +## Building and running a litmus test + +In this guide, we use `MP` (Message Passing), a popular litmus test +which demonstrates the communication pattern between a sender (P0) and +a receiver (P1_ process of a message `x`. There is also variable `y` +which is a flag, the sender sets it after setting the message `x` and +the receiver reads it before reading the message `x`. The test also +specifies a condition after the execution of the test which is +validated when P1 reads the initial value of message `x` (0) and the +new value of flag `y` (1). + +``` +AArch64 MP +"PodWW Rfe PodRR Fre" +Generator=diyone7 (version 7.56) +Prefetch=0:x=F,0:y=W,1:y=F,1:x=T +Com=Rf Fr +Orig=PodWW Rfe PodRR Fre +{ +0:X1=x; 0:X3=y; +1:X1=y; 1:X3=x; +} + P0 | P1 ; + MOV W0,#1 | LDR W0,[X1] ; + STR W0,[X1] | LDR W2,[X3] ; + MOV W2,#1 | ; + STR W2,[X3] | ; +exists (1:X0=1 /\ 1:X2=0) +``` + +Note: [diy7](http://diy.inria.fr/doc/gen.html) and +[diyone7]](http://diy.inria.fr/doc/gen.html) from the herdtools7 +toolsuite can systematically generate litmus tests. For example to +generate the MP litmus test: + + diyone7 -arch AArch64 PodWW Rfe PodRR Fre -name MP + +Assuming the file `MP.litmus` contains the test and KUT_DIR is the top +directory of kvm-unit-tests, we can use litmus7 to generate +the C sources: + + litmus7 -mach kvm-armv8.1 -variant precise -a 4 -o ${KUT_DIR}/litmus_tests MP.litmus + +To build the test: + + cd litmus-tests && make && cd - + +This will build the test in the file `litmus-tests/MP.flat` which you +can run like any other test: + + ./arm/run litmus-tests/MP.flat -smp 4 + +The test will print whether the condition of the test was observed +(`Allowed`), stats about the observed outcomes and metadata (e.g., +hash). + +``` +Test MP Allowed +Histogram (4 states) +19865 :>1:X0=0; 1:X2=1; +20885 *>1:X0=1; 1:X2=0; +975348:>1:X0=0; 1:X2=0; +983902:>1:X0=1; 1:X2=1; +Ok + +Witnesses +Positive: 20885, Negative: 1979115 +Condition exists (1:X0=1 /\ 1:X2=0) is validated +Hash=211d5b298572012a0869d4ded6a40b7f +Cycle=Rfe PodRR Fre PodWW +Generator=diycross7 (version 7.54+01(dev)) +Com=Rf Fr +Orig=PodWW Rfe PodRR Fre +Observation MP Sometimes 20885 1979115 +Time MP 3.19 +``` + +## References + +https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/expanding-memory-model-tools-system-level-architecture +https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/running-litmus-tests-on-hardware-litmus7 +http://diy.inria.fr/doc/litmus.html +https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/generate-litmus-tests-automatically-diy7-tool +http://diy.inria.fr/doc/gen.html -- 2.25.1
