Commuter is an automated scalability testing tool that hunts down unnecessary sharing in your code. Unlike traditional scalability testing, Commuter doesn't require handcrafted workloads or even multicore hardware. Starting with a high-level software interface model written in Python -- not some esoteric specification language -- Commuter automatically generates thousands of test cases for your interface and tests your implementation to root out the exact causes and locations of unnecessary, scalability-limiting sharing.

Commuter is currently a research prototype. It has been used to successfully analyze an 18 call model of the POSIX file system and virtual memory APIs and test the scalability of these calls in both Linux and our research OS kernel, sv6.

Check out Commuter's home page.

To simplify getting up and running, Commuter includes a "setup" script that can download and build all of Commuter's unusual dependencies with default configurations, as well as both sv6 and Mtrace-enabled Linux. You can run ./setup all, then jump straight to "Running the POSIX model" below. You can run ./setup with different arguments to install just some of the components.

Commuter depends on several other software packages, which themselves depend on other packages. You can either use Commuter's setup script to install these, or install them yourself.

• Z3 - Z3 is available from https://github.com/Z3Prover/z3 . As of this writing you'll need a nightly build, since Commuter depends on several bug fixes that are not in the stable 4.3.0 release. You can download pre-built nightlies for various OSs from Z3's home page, or clone their unstable branch.

  You may either install Z3 system-wide, or set the environment variables LD_LIBRARY_PATH and PYTHONPATH to the local installation of Z3 before running Commuter.

  The results in the SOSP '13 paper were generated with Z3 commit a60b53bfd from the unstable branch, but it's likely that any nightly build will work.

• mtrace - Mtrace is our modified version of QEMU that Commuter uses to run tests and detect sharing in OS kernels. Mtrace supports many other types of analyses, too, so it lives in a separate repository at

    git clone https://github.com/aclements/mtrace.git
  

  See mtrace's README.md for build instructions.

Running an operating system in Commuter requires a small amount of special support (specifically, hypercalls to mtrace). Commuter has been used with the following operating systems:

• Linux - The one and only. Our mtrace-enabled version of Linux can be found at

    git clone https://github.com/aclements/linux-mtrace.git
  

  See the README.md in the mtrace repository for build instructions and more information on using mtrace with Linux.

  Note that the we use an unconventional Linux setup. To keep the virtual machine minimal, we run it with no disk, completely from an initramfs. However, the initramfs does not contain a typical Linux user-space; to keep the sv6 and Linux environments as similar as possible, the initramfs contains the sv6 user-space, compiled for Linux. This is probably not the best setup in the long run, but it was expedient.

• sv6 - The scalable POSIX-like operating system we built with the help of Commuter. sv6 includes the RadixVM virtual memory system and the ScaleFS file system, published in EuroSys '13 and SOSP '13, respectively. sv6 can be found at

    git clone https://github.com/aclements/sv6.git
  

The setup script will download and build all of Commuter's dependencies and both operating systems. However, if you do this by hand,

1. Make sure mtrace is checked out in ext/mtrace and that you've compiled the mtrace version of QEMU as well as the tools in ext/mtrace/mtrace-tools.

2. Make sure sv6 is checked out in ext/sv6. You don't need to compile it, since the below instructions compile it with special options.

3. Make sure linux-mtrace is checked out in ext/linux-mtrace and compiled.

You can of course use a directory other than ext, but the directions below assume dependencies are checked out in ext.

Commuter consists of several separate components designed to make it easy to run (or re-run) just parts of the Commuter process.

• spec.py is the main entry point of Commuter, spec.py runs a model and its test generator and optionally produces commutativity conditions, test case code, and a machine-readable "model.out" summary of all explored paths and tests. spec.py can also optionally analyze interface idempotence.

• par-spec.py is a parallel driver for spec.py. Takes all the same arguments as spec.py.

• split-testgen.py splits test case code output into several files to enable parallel compilation.

• par-mtrace.py is a driver for running an OS kernel on the generated tests under mtrace to produce a memory access log.

• par-mscan.py is a driver for processing memory access logs to produce access conflict reports.

Commuter comes with several models. The main POSIX file system and virtual memory model is models.fs. There are also several toy models under models/.

There are several tools for analyzing output files under tools/.

• profile generates statistics on a "model.out" file (and optionally its delta from another "model.out" file).

• idem slices and dices idempotence data in "model.out" files in various ways.

• make-heatmaps generates heat map figures from mscan output in either SVG or TikZ format.

There is a web-based interactive data visualizer in viewer/. See its README.

# Run model; go get lunch
./par-spec.py models.fs -t testgen.c -m model.out --max-tests-per-path 500
# Split testgen.c for parallel build
./split-testgen.py -d ext/sv6/libutil < testgen.c

Neither Linux nor sv6 support testing reboot, so if your goal is only to examine cache line sharing, you can speed up spec.py by passing -f '!reboot'.

Furthermore, sv6 does not have an on-disk file system, so sync and fsync are no-ops in sv6. To disable test generation for these as well, pass -f '!reboot,!sync,!fsync' to spec.py.

cd ext/sv6
make HW=mtrace RUN='fstest -t; halt' mtrace.out
../mtrace/mtrace-tools/mscan --check-testcases --kernel o.mtrace/kernel.elf > mscan-sv6.out

cd ext/sv6
../../par-mtrace.py -m xv6
../../par-mscan.py --kernel o.mtrace/kernel.elf > mscan-sv6.out

cd ext/sv6
# Build the Linux initramfs for mtrace
make HW=linuxmtrace
# Run Linux kernel with tracing
make HW=linuxmtrace KERN=../linux-mtrace/arch/x86_64/boot/bzImage RUN='fstest -t;halt' mtrace.out
# Check sharing
../mtrace/mtrace-tools/mscan --kernel ../linux-mtrace/vmlinux --check-testcases > mscan-linux.out

cd ext/sv6
../../par-mtrace.py -m linux
../../par-mscan.py --kernel ../linux-mtrace/vmlinux > mscan-linux.out

This requires an mtrace kernel compiled with CONFIG_DEVTMPFS=y, CONFIG_BLK_DEV_RAM=y, and support for the desired file system.

cd ext/sv6
../../par-mtrace.py -m linux --fs-type ext4
../../par-mscan.py --kernel ../linux-mtrace/vmlinux > mscan-linux.out

Now you can examine mscan-sv6.out or mscan-linux.out for unnecessary sharing, or use the tools in tools/ to generate summaries, or fire up the interactive viewer in viewer/.