LUKS decryption taking an unreasonably long time?

[Aleksejs Popovs]

Hi,

Just installed GRUB on my new laptop and found the new cryptodisk 
feature. It seemed super convenient, so I enabled it, but what I noticed 
was that GRUB takes an unreasonably long time to actually decrypt the 
disk --- it takes approximately 10 seconds from the time I enter my 
passphrase until GRUB says "Slot 0 opened". For comparison, booting the 
system itself (which involves opening the slot again) takes less than a 
second.

Does anyone have any idea about why it is so slow and what I can do 
about it? I'd be happy to at least manage to profile it somehow, e.g. by 
enabling debugging output and looking at whether the slow part is the 
PBKDF, the key recovery, or something else, but I don't know how to 
enable debug mode, since this happens before grub.cfg can be read.

Thanks!
-Aleksejs