Quickstart Guide

This quickstart guide is designed for LLVM developers who are primarily interested in using LNT to test compilers using the LLVM test-suite.


The first thing to do is to checkout install the LNT software itself. The following steps should suffice on any modern Unix variant:

  1. Install virtualenv, if necessary:

    sudo easy_install virtualenv

    virtualenv is a standard Python tool for allowing the installation of Python applications into their own sandboxes, or virtual environments.

  2. Create a new virtual environment for the LNT application:

    virtualenv ~/mysandbox

    This will create a new virtual environment at ~/mysandbox.

  3. Checkout the LNT sources:

    git clone https://github.com/llvm/llvm-lnt.git ~/lnt
  4. Install LNT into the virtual environment:

    ~/mysandbox/bin/python ~/lnt/setup.py develop

    We recommend using develop instead of install for local use, so that any changes to the LNT sources are immediately propagated to your installation. If you are running a production install or care a lot about stability, you can use install which will copy in the sources and you will need to explicitly re-install when you wish to update the LNT application.

That’s it!

Running Tests

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

  1. 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.

  2. 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 /tmp/BAR \
      --cc ~/llvm.obj.64/Release+Asserts/bin/clang \
      --cxx ~/llvm.obj.64/Release+Asserts/bin/clang++ \
      --test-suite ~/llvm-test-suite \
      --cmake-cache Release

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

  3. On most systems, the execution time results will be a bit noisy. There are a range of things you can do to reduce noisiness (with LNT runtest test-suite command line options when available between brackets):

    • Only build the benchmarks in parallel, but do the actual running of the benchmark code at most one at a time. (--threads 1 --build-threads 6). Of course, when you’re also interested in the measured compile time, you should also build sequentially. (--threads 1 --build-threads 1).
    • When running under linux: Make lnt use linux perf to get more accurate timing for short-running benchmarks (--use-perf=1)
    • Pin the running benchmark to a specific core, so the OS doesn’t move the benchmark process from core to core. (Under linux: --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. (--benchmarking-only)
    • Make sure each program gets run multiple times, so that LNT has a higher chance of recognizing which programs are inherently noisy (--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.

You can create a local LNT instance with, e.g.:

lnt create ~/myperfdb

This will create an LNT instance at ~/myperfdb which includes the configuration of the LNT application and a SQLite database for storing the results.

Once you have a local instance, you can either submit results directly with:

lnt import ~/myperfdb SANDBOX/test-<stamp>/report.json

or as part of a run with:

lnt runtest --submit ~/myperfdb nt ... arguments ...

Once you have submitted results into a database, you can run the LNT web UI with:

lnt runserver ~/myperfdb

which runs the server on http://localhost:8000 by default.

In the future, LNT will grow a robust set of command line tools to allow investigation of performance results without having to use the web UI.