docs/linux_faster_builds.md

# Tips for improving build speed on Linux

This list is sorted such that the largest speedup is first; see
[Linux build instructions](linux_build_instructions.md) for context and
[Faster Builds](common_build_tasks.md) for non-Linux-specific techniques.

[TOC]

## General configuration

The [GN build configuration](https://www.chromium.org/developers/gn-build-configuration)
page discusses a number of options that will speed up your build. In particular:

    is_component_build = true
    enable_nacl = false
    symbol_level = 0
    remove_webcore_debug_symbols = true

## Use goma

If you work at Google, you can use goma for distributed builds; this is similar
to [distcc](http://en.wikipedia.org/wiki/Distcc). See [go/ma](http://go/ma) for
documentation.

Even without goma, you can do distributed builds with distcc (if you have access
to other machines), or a parallel build locally if have multiple cores.

Whether using goma, distcc, or parallel building, you can specify the number of
build processes with `-jX` where `X` is the number of processes to start.

## Use Icecc

[Icecc](https://github.com/icecc/icecream) is the distributed compiler with a
central scheduler to share build load. Currently, many external contributors use
it. e.g. Intel, Opera, Samsung.

When you use Icecc, you need to [set some GN variables](https://www.chromium.org/developers/gn-build-configuration).

    linux_use_bundled_binutils = false

The `-B` option is not supported.
[relevant commit](https://github.com/icecc/icecream/commit/b2ce5b9cc4bd1900f55c3684214e409fa81e7a92)

    linux_use_debug_fission = false

[debug fission](http://gcc.gnu.org/wiki/DebugFission) is not supported.
[bug](https://github.com/icecc/icecream/issues/86)

    is_clang = false

Icecc doesn't support clang yet.

    use_sysroot = false

Icecc doesn't work with sysroot.

Using the system linker is necessary when using glibc 2.21 or newer. See
[related bug](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=808181).
Previously these instructions listed the linux_use_bundled_gold GYP variable
which no longer exists. If you know about this, please update or delete this
section.

## WebKit

### Build WebKit without debug symbols

WebKit is about half our weight in terms of debug symbols. (Lots of templates!)
If you're working on UI bits where you don't care to trace into WebKit you can
cut down the size and slowness of debug builds significantly by building WebKit
without debug symbols.

Set the GN build arg `remove_webcore_debug_symbols=true` (to edit build args
run `gn args out/foo` where `out/foo` is your build directory).

## Tune ccache for multiple working directories

(Ignore this if you use goma.)

Increase your ccache hit rate by setting `CCACHE_BASEDIR` to a parent directory
that the working directories all have in common (e.g.,
`/home/yourusername/development`). Consider using
`CCACHE_SLOPPINESS=include_file_mtime` (since if you are using multiple working
directories, header times in svn sync'ed portions of your trees will be
different - see
[the ccache troubleshooting section](http://ccache.samba.org/manual.html#_troubleshooting)
for additional information). If you use symbolic links from your home directory
to get to the local physical disk directory where you keep those working
development directories, consider putting

    alias cd="cd -P"

in your `.bashrc` so that `$PWD` or `cwd` always refers to a physical, not
logical directory (and make sure `CCACHE_BASEDIR` also refers to a physical
parent).

If you tune ccache correctly, a second working directory that uses a branch
tracking trunk and is up to date with trunk and was gclient sync'ed at about the
same time should build chrome in about 1/3 the time, and the cache misses as
reported by `ccache -s` should barely increase.

This is especially useful if you use `git-new-workdir` and keep multiple local
working directories going at once.

## Using tmpfs

You can use tmpfs for the build output to reduce the amount of disk writes
required. I.e. mount tmpfs to the output directory where the build output goes:

As root:

    mount -t tmpfs -o size=20G,nr_inodes=40k,mode=1777 tmpfs /path/to/out

*** note
**Caveat:** You need to have enough RAM + swap to back the tmpfs. For a full
debug build, you will need about 20 GB. Less for just building the chrome target
or for a release build.
***

Quick and dirty benchmark numbers on a HP Z600 (Intel core i7, 16 cores
hyperthreaded, 12 GB RAM)

*   With tmpfs:
    *   12m:20s
*   Without tmpfs
    *   15m:40s