Distributed sccache (sccache-dist)¶
sccache is a ccache-like tool written in rust.
Distributed sccache (also referred to as sccache-dist) is being rolled out to Mozilla offices as a replacement for icecc. The steps for setting up your machine as an sccache-dist server as well as distributing your build to servers in your office are detailed below.
In addition to improved security properties, distributed sccache offers distribution and caching of rust compilation, so it should be an improvement above and beyond what we see with icecc. Build servers run on Linux and distributing builds is currently supported from Linux, macOS, and Windows.
Steps for distributing a build as an sccache-dist client¶
Start by following the instructions at https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#configure-a-client
to configure your sccache distributed client.
NOTE If you’re distributing from Linux a toolchain will be packaged
automatically and provided to the build server. If you’re distributing from
Windows or macOS, start by using the cross-toolchains provided by
./mach bootstrap rather than attempting to use
sccache 0.2.12 or above is recommended, and the auth section of your config
[dist.auth] type = "mozilla"
The scheduler url to use is:
https://sccache1.corpdmz.<OFFICE>.mozilla.com, where <OFFICE> is, for instance, sfo1. A complete list of office short names to be used can be found in the Office Addressing Schemes spreadsheet.
To use distributed sccache from a Mozilla office, you must be on the corporate network. Use the
Mozillassid for wireless. The corp vlan is the default if wired.
If you’re compiling from a macOS client, there are a handful of additional considerations outlined here: https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#considerations-when-distributing-from-macos.
./mach bootstrapto download prebuilt toolchains to
~/.mozbuild/rustc-dist-toolchain.tar.xz. This is an example of the paths that should be added to your client config to specify toolchains to build on macOS, located at
[[dist.toolchains]] type = "path_override" compiler_executable = "/path/to/home/.rustup/toolchains/stable-x86_64-apple-darwin/bin/rustc" archive = "/path/to/home/.mozbuild/rustc-dist-toolchain.tar.xz" archive_compiler_executable = "/builds/worker/toolchains/rustc/bin/rustc" [[dist.toolchains]] type = "path_override" compiler_executable = "/path/to/home/.mozbuild/clang/bin/clang" archive = "/path/to/home/.mozbuild/clang-dist-toolchain.tar.xz" archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang" [[dist.toolchains]] type = "path_override" compiler_executable = "/path/to/home/.mozbuild/clang/bin/clang++" archive = "/path/to/home/.mozbuild/clang-dist-toolchain.tar.xz" archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang"
Note that the version of
rustc-dist-toolchain.tar.xzmust match the version of
rustcused locally. The distributed archive will contain the version of
rustcused by automation builds, which may lag behind stable for a few days after Rust releases, which is specified by the task definition in this file. For instance, to specify 1.37.0 rather than the current stable, run
rustup toolchain add 1.37.0and point to
~/.rustup/toolchains/1.37.0-x86_64-apple-darwin/bin/rustcin your client config.
The build system currently requires an explicit target to be passed with
export HOST_CFLAGS="--target=x86_64-apple-darwin16.0.0" export HOST_CXXFLAGS="--target=x86_64-apple-darwin16.0.0"
Compiling from a Windows client is supported but hasn’t seen as much testing as other platforms. The following example mozconfig can be used as a guide:
ac_add_options CCACHE=~/.mozbuild/sccache/sccache.exe export CC="~/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" export CXX="~/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" export HOST_CC="~/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl" export HOST_CXX="~/.mozbuild/clang/bin/clang-cl.exe --driver-mode=cl"
The client config should be located at
~/AppData/Roaming/Mozilla/sccache/config/config, and as on macOS custom toolchains should be obtained with
./mach bootstrapand specified in the client config, for example:
[[dist.toolchains]] type = "path_override" compiler_executable = "C:/Users/<USER>/.mozbuild/clang/bin/clang-cl.exe" archive = "C:/Users/<USER>/.mozbuild/clang-dist-toolchain.tar.xz" archive_compiler_executable = "/builds/worker/toolchains/clang/bin/clang" [[dist.toolchains]] type = "path_override" compiler_executable = "C:/Users/<USER>/.rustup/toolchains/stable-x86_64-pc-windows-msvc/bin/rustc.exe" archive = "C:/Users/<USER>/.mozbuild/rustc-dist-toolchain.tar.xz" archive_compiler_executable = "/builds/worker/toolchains/rustc/bin/rustc"
Add the following to your mozconfig:
If you’re compiling from a macOS client, you might need some additional configuration:
# Set the target flag to Darwin export CFLAGS="--target=x86_64-apple-darwin16.0.0" export CXXFLAGS="--target=x86_64-apple-darwin16.0.0" export HOST_CFLAGS="--target=x86_64-apple-darwin16.0.0" export HOST_CXXFLAGS="--target=x86_64-apple-darwin16.0.0" # Specify the macOS SDK to use ac_add_options --with-macos-sdk=/path/to/MacOSX-SDKs/MacOSX10.11.sdk
When attempting to get your client running, the output of
sccache -sshould be consulted to confirm compilations are being distributed. To receive helpful logging from the local daemon in case they aren’t, run
SCCACHE_NO_DAEMON=1 RUST_LOG=sccache=trace path/to/sccache --start-serverin a terminal window separate from your build prior to building.
./mach build -j<value>with an appropriately large
sccache --dist-statusshould provide the number of cores available to you (or a message if you’re not connected). In the future this will be integrated with the build system to automatically select an appropriate value.
This should be enough to distribute your build and replace your use of icecc. Bear in mind there may be a few speedbumps, and please ensure your version of sccache is current before investigating further. Please see the common questions section below and ask for help if anything is preventing you from using it over email (dev-builds), on slack in #sccache, or in #build on irc.
Steps for setting up a server¶
Build servers must run linux and use bubblewrap 0.3.0+ for sandboxing of compile processes. This requires a kernel 4.6 or greater, so Ubuntu 18+, RHEL 8, or similar.
./mach artifact toolchain --from-build linux64-sccacheto acquire a recent version of
sccache-dist. Please use a
sccache-distbinary acquired in this fashion to ensure compatibility with statically linked dependencies.
Collect the IP of your builder and request assignment of a static IP in a bug filed in NetOps :: Other This bug should include your office (SFO, YVR, etc.), your MAC address, and a description of why you want a static IP (“To serve as an sccache builder” should be sufficient).
sccachesection of https://login.mozilla.com to generate an auth token for your builder.
The instructions at https://github.com/mozilla/sccache/blob/master/docs/DistributedQuickstart.md#configure-a-build-server should contain everything else required to configure and run the server.
NOTE Port 10500 will be used by convention for builders in offices. Please use port 10500 in the
public_addrsection of your builder config.
Extra logging may be helpful when setting up a server. To enable logging, run your server with
sudo env RUST_LOG=sccache=trace ~/.mozbuild/sccache/sccache-dist server --config ~/.config/sccache/server.conf(or similar). NOTE
sudomust come before setting environment variables for this to work.
As when configuring a client, the scheduler url to use is:
https://sccache1.corpdmz.<OFFICE>.mozilla.com, where <OFFICE> is an office abbreviation found here.
My build is still slow: scache-dist can only do so much with parts of the build that aren’t able to be parallelized. To start debugging a slow build, ensure the “Successful distributed compilations” line in the output of
sccache -sdominates other counts. For a full build, at least a 2-3x improvement should be observed.
My build output is incomprehensible due to a flood of warnings: clang will treat some warnings differently when it’s fed preprocessed code in a separate invocation (preprocessing occurs locally with sccache-dist). Adding
rewrite_includes_only = trueto the
distsection of your client config will improve this; however, setting this will cause build failures with a commonly deployed version of
glibc. This option will default to
trueonce the fix is more widely available. Details of this fix can be found in this patch.
My build fails with a message about incompatible versions of rustc between dependent crates: if you’re using a custom toolchain check that the version of rustc in your
rustc-dist-toolchain.tar.xzis the same as the version you’re running locally.