Speeding up Portage and Kernel Compiling

Ever get annoyed by Gentoo’s forever-lasting compiling? Here is few tricks I found that really helps when surfing through gentoo-wiki.com.

Speedup compiling using tmpfs

To speed up Portage compiling, the trick here is to mount a ramdisk at Portage temp compile directory. Everything in that directory will be placed onto RAM instead of going to disk, therefore greatly improves speed.

This is the time needed to compile xorg-server.

Before:

real    9m18.899s
user    9m49.958s
sys    4m18.195s

After:

real    6m48.731s
user    5m9.471s
sys    4m6.079s

Impressive eh? Its a 33% speed up. Since everything is placed in RAM, when compiling very large package (namely openoffice) you might get this message.

IOError: [Errno 28] No space left on device

It means we have ran out of space for ramdisk. Unmount the ramdisk and proceed with emerge.

gentoo ~ # umount /var/tmp/portage/
gentoo ~ # emerge something
Calculating dependencies -
...
gentoo ~ # mount /var/tmp/portage/

Next, we can speed up kernel compiling by using ccache. Since most of the time kernel is compiled with minor changes, ccache would speed up the process dramatically by “re-using” files that are already compiled. Its quite troublesome to make CC=”ccache gcc” -j3 everytime you want to compile the kernel, we can write up a script that simplifies the process.

File: /sbin/compile-kernel

cd /usr/src/linux

mount /boot
make clean

make CC="ccache gcc" -j3 && \  # -jN for parallel compiling (follow N = number of core + 1)
make modules_install && \
make install && \              # this will install kernel to default /boot/vmlinuz symlink
module-rebuild rebuild && \    # / You might want to comment out these two lines if
update-modules                 # \ you dont have module-rebuild installed.

make clean
umount /boot

cd $OLDPWD

As root, chmod u+x /sbin/compile-kernel to make it executable. Edit the script if necessary. To (re)compile kernel, just issue compile-kernel to do so.

Enjoy the blazing fast compiling.

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Further reading:
Using ccache