According to the 2023’s Second Quarter Status Report boot optimizations speed up kernel boot process.

The developer Colin Percival implemented a mergesort algorithm instead of the 30+ year old bubblesort of SYSINITs.

Bubblesort is a sorting algortithm that compares each element of an array with the next one and sorts them, whereas mergesort divides the array into subarrays. This system boosted speed by a factor of 100x.

https://www.freebsd.org/status/report-2023-04-2023-06/#_boot_performance_improvements

https://cgit.freebsd.org/src/commit/?id=9a7add6d01f3c5f7eba811e794cf860d2bce131d

https://www.theregister.com/2023/08/29/freebsd_boots_in_25ms/