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diff --git a/tools/memory-model/README b/tools/memory-model/README new file mode 100644 index 000000000..dab389042 --- /dev/null +++ b/tools/memory-model/README @@ -0,0 +1,223 @@ + ===================================== + LINUX KERNEL MEMORY CONSISTENCY MODEL + ===================================== + +============ +INTRODUCTION +============ + +This directory contains the memory consistency model (memory model, for +short) of the Linux kernel, written in the "cat" language and executable +by the externally provided "herd7" simulator, which exhaustively explores +the state space of small litmus tests. + +In addition, the "klitmus7" tool (also externally provided) may be used +to convert a litmus test to a Linux kernel module, which in turn allows +that litmus test to be exercised within the Linux kernel. + + +============ +REQUIREMENTS +============ + +Version 7.52 or higher of the "herd7" and "klitmus7" tools must be +downloaded separately: + + https://github.com/herd/herdtools7 + +See "herdtools7/INSTALL.md" for installation instructions. + +Note that although these tools usually provide backwards compatibility, +this is not absolutely guaranteed. + +For example, a future version of herd7 might not work with the model +in this release. A compatible model will likely be made available in +a later release of Linux kernel. + +If you absolutely need to run the model in this particular release, +please try using the exact version called out above. + +klitmus7 is independent of the model provided here. It has its own +dependency on a target kernel release where converted code is built +and executed. Any change in kernel APIs essential to klitmus7 will +necessitate an upgrade of klitmus7. + +If you find any compatibility issues in klitmus7, please inform the +memory model maintainers. + +klitmus7 Compatibility Table +---------------------------- + + ============ ========== + target Linux herdtools7 + ------------ ---------- + -- 4.14 7.48 -- + 4.15 -- 4.19 7.49 -- + 4.20 -- 5.5 7.54 -- + 5.6 -- 5.16 7.56 -- + 5.17 -- 7.56.1 -- + ============ ========== + + +================== +BASIC USAGE: HERD7 +================== + +The memory model is used, in conjunction with "herd7", to exhaustively +explore the state space of small litmus tests. Documentation describing +the format, features, capabilities and limitations of these litmus +tests is available in tools/memory-model/Documentation/litmus-tests.txt. + +Example litmus tests may be found in the Linux-kernel source tree: + + tools/memory-model/litmus-tests/ + Documentation/litmus-tests/ + +Several thousand more example litmus tests are available here: + + https://github.com/paulmckrcu/litmus + https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/perfbook.git/tree/CodeSamples/formal/herd + https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/perfbook.git/tree/CodeSamples/formal/litmus + +Documentation describing litmus tests and now to use them may be found +here: + + tools/memory-model/Documentation/litmus-tests.txt + +The remainder of this section uses the SB+fencembonceonces.litmus test +located in the tools/memory-model directory. + +To run SB+fencembonceonces.litmus against the memory model: + + $ cd $LINUX_SOURCE_TREE/tools/memory-model + $ herd7 -conf linux-kernel.cfg litmus-tests/SB+fencembonceonces.litmus + +Here is the corresponding output: + + Test SB+fencembonceonces Allowed + States 3 + 0:r0=0; 1:r0=1; + 0:r0=1; 1:r0=0; + 0:r0=1; 1:r0=1; + No + Witnesses + Positive: 0 Negative: 3 + Condition exists (0:r0=0 /\ 1:r0=0) + Observation SB+fencembonceonces Never 0 3 + Time SB+fencembonceonces 0.01 + Hash=d66d99523e2cac6b06e66f4c995ebb48 + +The "Positive: 0 Negative: 3" and the "Never 0 3" each indicate that +this litmus test's "exists" clause can not be satisfied. + +See "herd7 -help" or "herdtools7/doc/" for more information on running the +tool itself, but please be aware that this documentation is intended for +people who work on the memory model itself, that is, people making changes +to the tools/memory-model/linux-kernel.* files. It is not intended for +people focusing on writing, understanding, and running LKMM litmus tests. + + +===================== +BASIC USAGE: KLITMUS7 +===================== + +The "klitmus7" tool converts a litmus test into a Linux kernel module, +which may then be loaded and run. + +For example, to run SB+fencembonceonces.litmus against hardware: + + $ mkdir mymodules + $ klitmus7 -o mymodules litmus-tests/SB+fencembonceonces.litmus + $ cd mymodules ; make + $ sudo sh run.sh + +The corresponding output includes: + + Test SB+fencembonceonces Allowed + Histogram (3 states) + 644580 :>0:r0=1; 1:r0=0; + 644328 :>0:r0=0; 1:r0=1; + 711092 :>0:r0=1; 1:r0=1; + No + Witnesses + Positive: 0, Negative: 2000000 + Condition exists (0:r0=0 /\ 1:r0=0) is NOT validated + Hash=d66d99523e2cac6b06e66f4c995ebb48 + Observation SB+fencembonceonces Never 0 2000000 + Time SB+fencembonceonces 0.16 + +The "Positive: 0 Negative: 2000000" and the "Never 0 2000000" indicate +that during two million trials, the state specified in this litmus +test's "exists" clause was not reached. + +And, as with "herd7", please see "klitmus7 -help" or "herdtools7/doc/" +for more information. And again, please be aware that this documentation +is intended for people who work on the memory model itself, that is, +people making changes to the tools/memory-model/linux-kernel.* files. +It is not intended for people focusing on writing, understanding, and +running LKMM litmus tests. + + +==================== +DESCRIPTION OF FILES +==================== + +Documentation/README + Guide to the other documents in the Documentation/ directory. + +linux-kernel.bell + Categorizes the relevant instructions, including memory + references, memory barriers, atomic read-modify-write operations, + lock acquisition/release, and RCU operations. + + More formally, this file (1) lists the subtypes of the various + event types used by the memory model and (2) performs RCU + read-side critical section nesting analysis. + +linux-kernel.cat + Specifies what reorderings are forbidden by memory references, + memory barriers, atomic read-modify-write operations, and RCU. + + More formally, this file specifies what executions are forbidden + by the memory model. Allowed executions are those which + satisfy the model's "coherence", "atomic", "happens-before", + "propagation", and "rcu" axioms, which are defined in the file. + +linux-kernel.cfg + Convenience file that gathers the common-case herd7 command-line + arguments. + +linux-kernel.def + Maps from C-like syntax to herd7's internal litmus-test + instruction-set architecture. + +litmus-tests + Directory containing a few representative litmus tests, which + are listed in litmus-tests/README. A great deal more litmus + tests are available at https://github.com/paulmckrcu/litmus. + + By "representative", it means the one in the litmus-tests + directory is: + + 1) simple, the number of threads should be relatively + small and each thread function should be relatively + simple. + 2) orthogonal, there should be no two litmus tests + describing the same aspect of the memory model. + 3) textbook, developers can easily copy-paste-modify + the litmus tests to use the patterns on their own + code. + +lock.cat + Provides a front-end analysis of lock acquisition and release, + for example, associating a lock acquisition with the preceding + and following releases and checking for self-deadlock. + + More formally, this file defines a performance-enhanced scheme + for generation of the possible reads-from and coherence order + relations on the locking primitives. + +README + This file. + +scripts Various scripts, see scripts/README. |