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ccache: make awesome

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Ciro Santilli
2018-09-14 18:13:34 +01:00
parent 9c5b5b40d4
commit e575f73d9b
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@@ -9205,48 +9205,6 @@ which gives:
uid=1000(user0) gid=1000(user0) groups=1000(user0)
....
=== ccache
We have link:https://buildroot.org/downloads/manual/manual.html#ccache[enabled ccached] builds by default.
`BR2_CCACHE_USE_BASEDIR=n` is used, which means that:
* absolute paths are used and GDB can find source files
* but builds are not reused across separated LKMC directories
ccache can considerably speed up builds when you:
* are switching between multiple configurations for a given package to bisect something out, as mentioned at: <<modify-kernel-config>>
* clean the build because things stopped working. We store the cache outside of this repository, so you can nuke away without fear
The default ccache environment variables are honored if you have them set, which we recommend you do. E.g., in your `.bashrc`:
....
export CCACHE_DIR=~/.ccache
export CCACHE_MAXSIZE="20G"
....
The choice basically comes down to:
* should I store my cache on my HD or SSD?
* how big is my build, and how many build configurations do I need to keep around at a time?
If you don't set it, the default is to use `~/.buildroot-ccache` with `5G`, which is a bit small for us.
I find it very relaxing to watch ccache at work with:
....
watch -n1 'make -C "$(./getvar buildroot_build_dir)" ccache-stats'
....
or if you have it installed on host and the environment variables exported simply with:
....
watch -n1 'ccache -s'
....
while a build is going on in another terminal and my cooler is humming. Especially when the hit count goes up ;-) The joys of system programming.
=== Add new Buildroot packages
First, see if you can't get away without actually adding a new package, for example:
@@ -9654,6 +9612,17 @@ cp config.example data/config
and then edit the `data/config` file to your needs.
=== Build the documentation
You don't need to depend on GitHub:
....
./build-doc
xdg-open out/README.html
....
Source: link:build-doc[]
=== Clean the build
You did something crazy, and nothing seems to work anymore?
@@ -9702,16 +9671,46 @@ Verify with:
ls "$(./getvar build_dir)"
....
=== Build the documentation
=== ccache
You don't need to depend on GitHub:
link:https://en.wikipedia.org/wiki/Ccache[ccache] <<benchmark-builds,might>> save you a lot of re-build when you decide to <<clean-the-build>> or create a new <<build-variants,build variant>>.
We have ccache enabled for everything we build by default.
However, you likely want to add the following to your `.bashrc` to take better advantage of `ccache`:
....
./build-doc
xdg-open out/README.html
export CCACHE_DIR=~/.ccache
export CCACHE_MAXSIZE="20G"
....
Source: link:build-doc[]
We cannot automate this because you have to decide:
* should I store my cache on my HD or SSD?
* how big is my build, and how many build configurations do I need to keep around at a time?
If you don't those variables it, the default is to use `~/.buildroot-ccache` with `5G`, which is a bit small for us.
To check if `ccache` is working, run this command while a build is running on another shell:
....
watch -n1 'make -C "$(./getvar buildroot_build_dir)" ccache-stats'
....
or if you have it installed on host and the environment variables exported simply with:
....
watch -n1 'ccache -s'
....
and then watch the miss or hit counts go up.
We have link:https://buildroot.org/downloads/manual/manual.html#ccache[enabled ccached] builds by default.
`BR2_CCACHE_USE_BASEDIR=n` is used for Buildroot, which means that:
* absolute paths are used and GDB can find source files
* but builds are not reused across separated LKMC directories
=== Simultaneous runs