Ccache в Gentoo Linux

Что такое ccache? ccache - это быстрый кэш компилятора. Временные файлы, которые будут созданы во время компиляции программы будут закэшированы, в результате чего во время обновления установленного программного обеспечения, время , затраченное на компиляцию программного значительно cокращается. Компиляция программ из исходных текстов часто занимает очень много времени, особенно на слабых машинах. Если Вы имеете несколько компьютеров объединенных в сеть, то тогда этот процесc можно ускорить. В этой статье представлен способ значительного ускорения компиляции программ, средствами ccache и distcc.

ccache использует опцию GCC -E  и хэш для определения можно ли взять результат компиляции из кэша. Эффект от использования заключается в ускорении компиляции часто компилируемого кода в 5-10 раз.

Установка

1. Убедитесь что используемая версия portage больше чем 2.0.46-r11: emerge --version
2. Установите ccache: emerge -av dev-util/ccache

Расположение файлов

При установке ccache как root, создаются такие файлы и папки:

• /usr/lib/ccache - дом для файлов откуда portage будет запускаться вместо обычных компиляторов
• /usr/bin/ccache - запускаемые файлы ccache
• /root/.ccache - харнилище cache

Когда ccache устанавливается для пользователей, дополнительно создаётся ещё одна папка:

• /var/tmp/ccache - хранилище cache

Solid information on this structure has proven difficult to come by and anyone who can provide an authorative answer should edit this page to do so.

However it seems that /var/tmp/ccache is unique to Gentoo, and should be chosen over /root/.ccache to store the cache.

Configuration

$ ls -l /usr/lib/ccache/bin
...
lrwxrwxrwx 1 root portage 15  Mar 6 i686-pc-linux-gnu-c++ -> /usr/bin/ccache
lrwxrwxrwx 1 root portage 15  Mar 6 i686-pc-linux-gnu-g++ -> /usr/bin/ccache
lrwxrwxrwx 1 root portage 15  Mar 6 i686-pc-linux-gnu-gcc -> /usr/bin/ccache
...

The 3 files are links, all of them pointing to: /usr/bin/ccache

When portage seeks to compile a package, it of course looks for the relevant compiler. However we don't want portage to go direct to the compiler, rather we want the compiler accessed through ccache. Thus we have a number of symlinks in the ccache directory which bear names that correspond to the various c and c++ compilers that portage looks for. With ccache enabled, Portage follows the path to /usr/lib/ccache/bin, and thus one of these files is invoked instead of one of the actual compilers. As you will see from the box above, all of these files are merely links to the ccache executable, (/usr/bin/ccache), which itself will call the genuine compilers.

Configuration takes place within /etc/make.conf

...
FEATURES="ccache"
CCACHE_DIR="/var/tmp/ccache/"
CCACHE_SIZE="2G"
...

1. Most importantly we need /etc/make.conf to inform portage to look for and use ccache. This is achieved by the first of the three lines above. If you already have some features set, naturally just add "ccache" to the list.
   • If you also use DistCC, be sure you add the "ccache" option first and "distcc" second in your features list to take full advantage of both.
2. The CCACHE_DIR environment variable specifies where ccache will keep its cached compiler output.
3. The 3rd line sets the maximum space that is allocated to caching compilations. At the time of writing the default maximum size is 976.6M. If you can afford the space you may well want to allow for more as in the example.
   • The ccache stats won't update to show your chosen CACHE_SIZE until after the emerge that follows your change in specification.
   • You can also set the cache size by employing the -M option described on ccache's man page. However, if you have a CCACHE_SIZE value set in /etc/make.conf, it will overwite previously set values from as soon as you next emerge.

Execution

Now, for the purpose of testing, emerge something small...

To ensure that ccache was running, pull up the ccache stats afterwards with: ccache -s

If you're using the CCACHE_DIR in /var/tmp/ccache you need to add that variable to the command string as shown below.

CCACHE_DIR="/var/tmp/ccache" ccache -s
/* The output will look something like this if it's working */
cache hit                            189
cache miss                          1983
called for link                      159
multiple source files                  4
compile failed                        52
preprocessor error                     4
bad compiler arguments                 3
not a C/C++ file                     141
autoconf compile/link                357
unsupported compiler option           30
no input file                        145
files in cache                      3966
cache size                          30.1 Mbytes
max cache size                       2.0 Gbytes

If no space shows as used, your cache directory is still empty and it might be the case that ccache (when run direct rather than by Portage) is looking for the cache store in the wrong place. You can overcome this by declaring the location of the cache store system-wide. Update your profile to include the second line that we added to /etc/make.conf as follows:

 echo "CCACHE_DIR=\"/var/tmp/ccache\"" >> /etc/env.d/99local 
 env-update && source /etc/profile

Troubleshooting

ccache and Genkernel

Genkernel doesn't use ccache by default, even when you've enabled it for root. You can easily fix this by appending the --kernel_cc option to your genkernel call:

$ genkernel --kernel-cc=/usr/lib/ccache/bin/gcc --menuconfig all

A better way then this is to add a file to /etc/env.d called 02ccache with the following contents: PATH="/usr/lib/ccache/bin"

then run env-update, that way everything (including genkernel) will use the local ccache. If you want root to see the settings too, add ROOTPATH="/usr/lib/ccache/bin" to 02ccache as well.

ccache adjusts directory permissions

Apparently ccache will sometimes try to set the permissions of the ccache_dir after and before each emerge. Type this to fix that:

# chmod g+X -R /usr/lib/ccache

Источник: http://gentoo-wiki.com/TIP_Use_ccache

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