学步园

Linux Kernel: Speed Up Compilation

I have been having a hard time for the last few days in doing my
"Linux Kernel Assignment". No, programming is not the hardest part.
Waiting for the kernel to compile is the main problem. Its pathetically
the moment when you become the sitting duck. :). So here are some of
the things I came across to speed up the compilation.

1. Make sure you have ccache
   installed and configured. As the name suggests, ccache
   dramatically speeds up subsequent compilations by caching the object
   files. In most new Fedora distros, its enabled by default. You can
   check it by doing $which gcc
   . If it says something like /usr/lib/ccache/gcc
   , you are all set up. If not, try google,
   You can see see its status by issuing command $ccache -s
   . Its good to set the cache amount a bigger than default, so $ccache -M 2G
   will set the cache to 2GB which is enough for everyone.
2. Use gcc
   option -pipe
   whenever possible. Self explanatory, it uses pipes instead of temporary files.
3. If
   you have dual core or quad core processor and a lot of RAM, you'll
   notice that while compiling, only a fraction of your processor and RAM
   gets used. This is because there is only one compile process running at
   a time. You can specify multiple make
   jobs by passing parameter like this $make -j 2
   .
   Here, make will run at most 2 jobs at a time, taking full advantage of
   your multi-core CPU and RAM. Some argue on setting higher value, but I
   do not recommend it, as it likely to have negative effect because of
   the large amount of context switched in the CPU. People say that this
   approach leads to race conditions but I haven't bumped into any of that
   yet.
4. For Linux Kernel compilation, make sure you have CONFIG_DEBUG_KERNEL
   unset in .config
   file. If set, this builds your kernel with debugging symbol making your
   kernel a lot bigger and significantly longer to build. It will make
   kernel debugging impossible though, but when you are in a hurry, this
   really makes more sense. Also strip the .config
   file from
   any unnecessary drivers/modules you don't require, but this will
   require you to have a thorough knowledge about both your PC and running
   kernel.
5. For those with high speed network (ethernet or more), give a try to distcc
   ,
   that distributes the compilation among multiple machine. The
   configuration is quite straight forward. Check the references section
   for details. 
6. Try tmpfs
   . It enables you to mount
   any folder in your file system in RAM, so theoretically speeding up the
   compilation. Try mounting your build folder with tmpfs
   like this $sudo mount -t tmpfs -o size=500M,mode=0777 tmpfs /usr/src/linux-build
   .

Using
the above mentioned method, you can get a clean build of 2.6.29 kernel
in less than 15 minutes. Let me know if you have any problems or come
up with any better solutions.

References:

https://help.ubuntu.com/community/Kernel/Compile

http://www.linux.org/docs/ldp/howto/Modules/speedup.html

http://en.gentoo-wiki.com/wiki/Portage_TMPDIR_on_tmpfs

http://www.ibm.com/developerworks/linux/library/l-distcc.html