Linux boot time reduced by 0.035 seconds thanks to a one-line kernel patch — aligning the slab in the ACPI code makes Linux boot faster

Linux systems already boot relatively fast, but it’s never fast enough. So, when Linux engineer Colin Ian King (via Phoronix) discovered that aligning the slab in the ACPI code would make Linux boot faster, it was considered a win for the system.

According to King, “Enabling SLAB_HWCACHE_ALIGN for the ACPI object caches improves boot speed in the ACPICA core for object allocation and free’ing especially in the AML parsing and execution phases in boot. Testing with 100 boots shows an average boot saving in acpi_init of ~35000 usecs compared to the unaligned version. Most of the ACPI objects being allocated and free’d are of very short life times in the critical paths for parsing and execution, so the extra memory used for alignment isn’t too onerous.”

The 0.035-faster boot time might mean nothing for most users, especially as people won’t even feel a one-second change in loading times. But with Linux being an open-source system, many people with free time have been working on improving the OS, no matter how small. It has received multiple optimizations since the glory days of the netbook.

This slight decrease in boot times will have a more significant impact on data centers, many of which run on open-source Linux systems. This potentially minimizes downtime in servers that require 24/7 uptime and a 99.99% availability. The slight change could also affect millions of users, given the ubiquity of the operating system in many backend systems.

For example, 96.3% of the top 1,000,000 web servers use Linux, and over 460 of the top 500 supercomputers are powered by the operating system. IoT devices also prefer Linux, with a reported market share of 68% of all IoT devices in the wild. It’s also used as the primary OS of 70% of the web servers globally.

Although the average user is only familiar with Android, iOS, Windows, or macOS, these numbers show how much of our modern world is driven by this open-source operating system and its derivatives. Even though 0.035 might seem insignificant, if you multiply that by the billions of Linux devices, you’re potentially looking at days, months, and even years of operating hours saved.