Is that an interesting difference, though? At least on my machine, boot time is dominated by... grub loading the kernel and initramfs. Which is actually ridiculous when you consider it's a few dozen megabytes on a NVMe. I have't inveatigated what's up yet.

On a VM, where you don't have to deal with the incredible slowness of pre-boot hardware, that's a big speedup.

On a physical computer where you have to wait 15 seconds for the machine to post anyway, yeah it's not a big difference.

Certainly is to me! I build embedded Linux devices. Our current boottime from cold-boot to fully functioning is roughly 3 seconds. I would really like to get it lower and shaving off almost half a second would be amazing.

fyi a quick way to see this is with systemd-analyze

  systemd-analyze plot > bootplot.svg

  systemd-analyze critical-chain

  systemd-analyze blame

Systemd-analyze doesn't know about grub.

BIOS I/O calls are extremely slow. EFI boot-time services are significantly faster.

That's on a machine with EFI.