I use ubuntu on Dell Inspiron n4050.I have upgraded to ubuntu 12.04 from 10.04.
But now I find the system startup is a little slow and plymouth only show purple screen without logo during startup.
When I use dmesg, it shows such messages:

    [    2.497750] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
    [    2.603028] usb 2-1.6: new high-speed USB device number 3 using ehci_hcd
    [    2.715538] Initializing USB Mass Storage driver...
    [    2.715594] usbcore: registered new interface driver usb-storage
    [    2.715596] USB Mass Storage support registered.
    [   21.317843] Adding 2000892k swap on /dev/sda5.  Priority:-1 extents:1 across:2000892k
    [   21.323724] ADDRCONF(NETDEV_UP): eth0: link is not ready
    [   21.391450] udevd[431]: starting version 175

I wonder what it is doing between 2 second and 21 second. Is it related to being so slow?
I tried bootchart. It gave me a complex picture. Sorry I can't post it here. http://3.bp.blogspot.com/-7LX8T5uQvlw/UKhdFMVkp4I/AAAAAAAAADg/dtxePkE94mg/s320/lengzhen-ubuntu-precise-20121118-1.png

While ubuntu is booting , I also noticed that it appears:/tmp is not ready or present And sometimes follows *Stop saving kernel messages. Is this the reason dmesg lost output?