This is very interesting after I poke around i can actually see that the CPU hog for IRQ19 is used by "Intel ATA Controller" as i can see it during the system bootup and it scroll by the screen.
then I check my system BIOS and my on-board SATA controller is already using IDE mode (non AHCI mode). So i went and disable just about everything I can find under the BIOS related to AHCI or disk mode and access, but nothing will make the CPU hog of IRQ19 drop. So finally I decided to change my SATA controller from IDE mode to AHCI mode, then after a reboot, my CPU usage is down to about 0% now. So this is interesting that it should be set to AHCI mode on this hardware combination.
This has been a good learning experience.