4.5. About SBUs

Many people would like to know beforehand approximately how long it takes to compile and install each package. Because Linux From Scratch can be built on many different systems, it is impossible to provide absolute time estimates. The biggest package (gcc) will take approximately 5 minutes on the fastest systems, but could take days on slower systems! Instead of providing actual times, the Standard Build Unit (SBU) measure will be used instead.

The SBU measure works as follows. The first package to be compiled is binutils in Chapter 5. The time it takes to compile using one core is what we will refer to as the Standard Build Unit or SBU. All other compile times will be expressed in terms of this unit of time.

For example, consider a package whose compilation time is 4.5 SBUs. This means that if your system took 4 minutes to compile and install the first pass of binutils, it will take approximately 18 minutes to build the example package. Fortunately, most build times are shorter than one SBU.

SBUs are not entirely accurate because they depend on many factors, including the host system's version of GCC. They are provided here to give an estimate of how long it might take to install a package, but the numbers can vary by as much as dozens of minutes in some cases.

On some newer systems, the motherboard is capable of controlling the system clock speed. This can be controlled with a command such as powerprofilesctl. This is not available in LFS, but may be available on the host distro. After LFS is complete, it can be added to a system with the procedures at the BLFS power-profiles-daemon page. Before measuring the build time of any package it is advisable to use a system power profile set for maximum performance (and maximum power consumption). Otherwise the measured SBU value may be inaccurate because the system may react differently when building binutils-pass1 or other packages. Be aware that a significant inaccuracy can still show up even if the same profile is used for both packages because the system may respond slower if the system is idle when starting the build procedure. Setting the power profile to “performance” will minimize this problem. And obviously doing so will also make the system build LFS faster.

If powerprofilesctl is available, issue the powerprofilesctl set performance command to select the performance profile. Some distros provides the tuned-adm command for managing the profiles instead of powerprofilesctl, on these distros issue the tuned-adm profile throughput-performance command to select the throughput-performance profile.