Go in your device manager and check you controller properties and that should show you what mode you are in . you may already be in AHCI . If you find that this is so you will have to start trouble shooting the drive it self. And you can contact HP to see if they have a BIOS update.
Sily question But why ubuntu , and not Windows 7 64bit ?? I just upgraded a older DV9000, HP , Put in a WD 128gig SSD and a fresh copy of W7 64 , Now runs better than it ever did the OEM hard drives were 5400 RPMs , and even though this machine uses SATA 1.5 , Now I getting 138619 reads and136450 writes , before I was getting 41230 reads and 39876 writes , Thats about 3 times faster than the old HD, and the response time is 0.04Ms where the old HD was 18Ms. Performance is all about INOPS in & outs . You can also check UBUNTU may not support TRIM which is important for a SSD , Did you download the INTEL TOOL BOX and run the clean up??
Well if your stuck on that OS than you need to find out does it support TRIM, and does it support Intel's SSD TOOL BOX, If it does than you can optimize your SSD Manuely. you should run the tool box at lease once a week. Than use ATTO to test the SSD ,It's a free download just gogle it.