My German readers know that I work on an article series regarding a reasonable full encryption of customer related Linux laptops and virtual machines with dm-crypt/LUKS. Whilst experimenting with different configurations I found that all my naive assumptions regarding the boot time of fully encrypted systems on standard laptops were wrong.
The boot manager for Linux - Grub2 - can lead to unacceptable long boot times (> n * 10 secs) - despite much smaller and reasonable values for the time required by the kernel to open encrypted devices. Delay factors during boot of more than 7 to 8 are possible and have to be taken into account during the encryption setup.
In my case Grub2 appears to be dead slow regarding a distinct factor which determines the time required during a first boot phase until the graphical Grub menu with choices for bootable installations gets displayed. The time for later boot phases (loaded kernel with initrd-support, access to encrypted volumes by the kernel) is much, much shorter.
A quick test showed that Grub2 is inefficient with respect to the SHA512 and not to the core and aes-based symmetric decryption algorithm.