Importing zpool takes a long time on boot

[notthebee]

System information

Type	Version/Name
Distribution Name	Gentoo
Distribution Version	Stable with OpenRC
Linux Kernel	4.18.16-ck
Architecture	AMD64
ZFS Version	0.7.11
SPL Version	0.7.11

Describe the problem you're observing

I recently moved my Gentoo root to ZFS, and so far everything works great, except for one thing: importing zpool takes a long time (one-two minutes) on boot.

Also, zpool status shows "sda" instead of disk/by-id entry, not sure if that's relevant.

Include any warning/errors/backtraces from the system logs

zpool status:

  pool: gentoo
 state: ONLINE
  scan: none requested
config:

	NAME        STATE     READ WRITE CKSUM
	gentoo      ONLINE       0     0     0
	  sda       ONLINE       0     0     0

errors: No known data errors

zfs list:

NAME                      USED  AVAIL  REFER  MOUNTPOINT
gentoo                   83.0G   390G    96K  none
gentoo/ROOT              83.0G   390G    96K  none
gentoo/ROOT/boot         29.6M   390G  29.6M  /boot
gentoo/ROOT/gentoo       5.11G   390G  5.11G  /
gentoo/ROOT/home         65.3G   390G  65.3G  /home
gentoo/ROOT/tmp           128K   390G   128K  /tmp
gentoo/ROOT/usr          6.21G   390G  6.21G  /usr
gentoo/ROOT/usr_local    7.26M   390G  7.26M  /usr/local
gentoo/ROOT/usr_portage  4.50G   390G  4.50G  /usr/portage
gentoo/ROOT/var          1.76G   390G  1.76G  /var