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."
