Running Tests

Quickstart

To execute the LLVM test-suite using LNT, use the lnt runtest command. The information below should be enough to get you started, but see the sections below for more complete documentation.

  1. Install lnt as explained in the installation section.

  2. Make sure lit is installed, for example with pip install lit or via a monorepo installation accessible in your $PATH. By default, lnt will look for a binary named llvm-lit in your $PATH. Depending on how you install lit, you may have to point lnt to the right binary by using the --use-lit <path> flag in the command below.

  3. Checkout the LLVM test-suite, if you haven’t already:

    git clone https://github.com/llvm/llvm-test-suite.git llvm-test-suite

    You should always keep the test-suite directory itself clean (that is, never do a configure inside your test suite). Make sure not to check it out into the LLVM projects directory, as LLVM’s configure/make build will then want to automatically configure it for you.

  4. Execute the lnt runtest test-suite test producer, point it at the test suite and the compiler you want to test:

    lnt runtest test-suite --sandbox $PWD/sandbox            \
                       --cc clang                        \
                       --cxx clang++                     \
                       --test-suite $PWD/llvm-test-suite \
                       --cmake-cache Release

    The --sandbox argument is a path to where the test suite build products and results will be stored (inside a timestamped directory, by default).

    We recommend adding --build-tool-options "-k" (if you are using make) or --build-tool-options "-k 0" (if you are using ninja). This ensures that the build tool carries on building even if there is a compilation failure in one of the tests. Without these options, every test after the compilation failure will not be compiled and will be reported as a missing executable.

  5. If you already have a LNT server instance running, you can submit these results to it by passing --submit <path-or-URL-of-instance>.

  6. On most systems, the execution time results will be a bit noisy. There are a range of things you can do to reduce noise:

    • Only build the benchmarks in parallel, but do the actual running of the benchmark code at most one at a time (use --threads 1 --build-threads 6). Of course, when you’re also interested in the measured compile time, you should also build sequentially (use --threads 1 --build-threads 1).

    • When running on linux: Make lnt use perf to get more accurate timing for short-running benchmarks (use --use-perf=1).

    • Pin the running benchmark to a specific core, so the OS doesn’t move the benchmark process from core to core (on linux, use --make-param="RUNUNDER=taskset -c 1").

    • Only run the programs that are marked as a benchmark; some of the tests in the test-suite are not intended to be used as a benchmark (use --benchmarking-only).

    • Make sure each program gets run multiple times, so that LNT has a higher chance of recognizing which programs are inherently noisy (use --multisample=5).

    • Disable frequency scaling / turbo boost. In case of thermal throttling it can skew the results.

    • Disable as many processes or services as possible on the target system.

Viewing Results

By default, lnt runtest test-suite will show the passes and failures after doing a run, but if you are interested in viewing the result data in more detail you should install a local LNT instance to submit the results to. See the sections on running a server and importing data for instructions on how to do that.

Test Producers

On the client-side, LNT comes with a number of built-in test data producers. This documentation focuses on the LLVM test-suite (aka nightly test) generator, since it is the primary test run using the LNT infrastructure, but note that LNT also includes tests for other interesting pieces of data, for example Clang compile-time performance.

LNT also makes it easy to add new test data producers and includes examples of custom data importers (e.g., to import buildbot build information into) and dynamic test data generators (e.g., abusing the infrastructure to plot graphs, for example).

Built-in Tests

The built-in tests are designed to be run via the lnt tool. The following tools for working with built-in tests are available:

lnt showtests

List the available tests. Tests are defined with an extensible architecture. FIXME: Point at docs on how to add a new test.

lnt runtest [<run options>] <test name> ... test arguments ...

Run the named test. The run tool itself accepts a number of options which are common to all tests. The most common option is --submit=<url> which specifies the server to submit the results to after testing is complete. See lnt runtest --help for more information on the available options.

The remainder of the options are passed to the test tool itself. The options are specific to the test, but well behaved tests should respond to lnt runtest <test name> --help. The following section provides specific documentation on the built-in tests.

LLVM CMake test-suite

The llvm test-suite can be run with the test-suite built-in test.

Running the test-suite via CMake and lit uses a different LNT test:

rm -rf /tmp/BAR
lnt runtest test-suite                                \
     --sandbox /tmp/BAR                               \
     --cc ~/llvm.obj.64/Release+Asserts/bin/clang     \
     --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++  \
     --use-cmake=/usr/local/bin/cmake                 \
     --use-lit=~/llvm/utils/lit/lit.py                \
     --test-suite llvm-test-suite                     \
     --cmake-cache Release

Since the CMake test-suite uses lit to run the tests and compare their output, LNT needs to know the path to your LLVM lit installation. The test-suite holds some common configurations in CMake caches. The --cmake-cache flag and the --cmake-define flag allow you to change how LNT configures cmake for the test-suite run.

Capturing Linux perf profile info

When using the CMake driver in the test-suite, LNT can also capture profile information using linux perf. This can then be explored through the LNT webUI as demonstrated at http://blog.llvm.org/2016/06/using-lnt-to-track-performance.html .

To capture these profiles, use command line option --use-perf=all. A typical command line using this for evaluating the performance of generated code looks something like the following:

lnt runtest test-suite                  \
     --sandbox SANDBOX                  \
     --cc ~/bin/clang                   \
     --use-cmake=/usr/local/bin/cmake   \
     --use-lit=~/llvm/utils/lit/lit.py  \
     --test-suite llvm-test-suite       \
     --benchmarking-only                \
     --build-threads 8                  \
     --threads 1                        \
     --use-perf=all                     \
     --exec-multisample=5               \
     --run-under 'taskset -c 1'

Bisecting: --single-result and --single-result-predicate

The LNT driver for the CMake-based test suite comes with helpers for bisecting conformance and performance changes with llvmlab bisect.

llvmlab bisect is part of the zorg repository and allows easy bisection of some predicate through a build cache. The key to using llvmlab effectively is to design a good predicate command - one which exits with zero on ‘pass’ and nonzero on ‘fail’.

LNT normally runs one or more tests then produces a test report. It always exits with status zero unless an internal error occurred. The --single-result argument changes LNT’s behaviour - it will only run one specific test and will apply a predicate to the result of that test to determine LNT’s exit status.

The --single-result-predicate argument defines the predicate to use. This is a Python expression that is executed in a context containing several pre-set variables:

  • status - Boolean passed or failed (True for passed, False for failed).

  • exec_time - Execution time (note that exec is a reserved keyword in Python!)

  • compile (or compile_time) - Compilation time

Any metrics returned from the test, such as “score” or “hash” are also added to the context.

The default predicate is simply status - so this can be used to debug correctness regressions out of the box. More complex predicates are possible; for example exec_time < 3.0 would bisect assuming that a ‘good’ result takes less than 3 seconds.

Full example using llvmlab to debug a performance improvement:

llvmlab bisect --min-rev=261265 --max-rev=261369                            \
  lnt runtest test-suite                                                    \
    --cc '%(path)s/bin/clang'                                               \
    --sandbox SANDBOX                                                       \
    --test-suite /work/llvm-test-suite                                      \
    --use-lit lit                                                           \
    --run-under 'taskset -c 5'                                              \
    --cflags '-O3 -mthumb -mcpu=cortex-a57'                                 \
    --single-result MultiSource/Benchmarks/TSVC/Expansion-flt/Expansion-flt \
    --single-result-predicate 'exec_time > 8.0'

Producing Diagnositic Reports

The test-suite module can produce a diagnostic report which might be useful for figuring out what is going on with a benchmark:

lnt runtest test-suite                                  \
       --sandbox /tmp/BAR                               \
       --cc ~/llvm.obj.64/Release+Asserts/bin/clang     \
       --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++  \
       --use-cmake=/usr/local/bin/cmake                 \
       --use-lit=~/llvm/utils/lit/lit.py                \
       --test-suite llvm-test-suite                     \
       --cmake-cache Release                            \
       --diagnose --only-test SingleSource/Benchmarks/Stanford/Bubblesort

This will run the test-suite many times over, collecting useful information in a report directory. The report collects many things like execution profiles, compiler time reports, intermediate files, binary files, and build information.

Cross-compiling

The best way to run the test-suite in a cross-compiling setup with the cmake driver is to use cmake’s built-in support for cross-compiling as much as possible. In practice, the recommended way to cross-compile is to use a cmake toolchain file (see https://cmake.org/cmake/help/v3.0/manual/cmake-toolchains.7.html#cross-compiling)

An example command line for cross-compiling on an X86 machine, targeting AArch64 linux, is:

lnt runtest test-suite                                    \
       --sandbox SANDBOX                                  \
       --test-suite /work/llvm-test-suite                 \
       --use-lit lit                                      \
       --cppflags="-O3"                                   \
       --run-under=$HOME/dev/aarch64-emu/aarch64-qemu.sh  \
       --cmake-define=CMAKE_TOOLCHAIN_FILE:FILEPATH=$HOME/clang_aarch64_linux.cmake

The key part here is the CMAKE_TOOLCHAIN_FILE define. As you’re cross-compiling, you may need a –run-under command as the produced binaries probably won’t run natively on your development machine, but something extra needs to be done (e.g. running under a qemu simulator, or transferring the binaries to a development board). This isn’t explained further here.

In your toolchain file, it’s important to specify that the cmake variables defining the toolchain must be cached in CMakeCache.txt, as that’s where lnt reads them from to figure out which compiler was used when needing to construct metadata for the json report. An example is below. The important keywords to make the variables appear in the CMakeCache.txt are “CACHE STRING “” FORCE”:

$ cat clang_aarch64_linux.cmake
set(CMAKE_SYSTEM_NAME Linux )
set(triple aarch64-linux-gnu )
set(CMAKE_C_COMPILER /home/user/build/bin/clang CACHE STRING "" FORCE)
set(CMAKE_C_COMPILER_TARGET ${triple} CACHE STRING "" FORCE)
set(CMAKE_CXX_COMPILER /home/user/build/bin/clang++ CACHE STRING "" FORCE)
set(CMAKE_CXX_COMPILER_TARGET ${triple} CACHE STRING "" FORCE)
set(CMAKE_SYSROOT /home/user/aarch64-emu/sysroot-glibc-linaro-2.23-2016.11-aarch64-linux-gnu )
set(CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN /home/user/aarch64-emu/gcc-linaro-6.2.1-2016.11-x86_64_aarch64-linux-gnu )
set(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN /home/user/aarch64-emu/gcc-linaro-6.2.1-2016.11-x86_64_aarch64-linux-gnu )