Thanks for all your help. I ran into another problem.
 
My 16-core machine has a scsi/sata disk. I have enabled all important features related with scsi and sata.  I built 2.6.23 kernel on this machine. But the kernel always got crashed randomly. Sometimes it couldnot even boot, reporting some random errors,  like "segment violation, sleep for 40 seconds", or "Group volume VolGroup00 uses lvm2 metadata: read-only", then jump to a strange login window that I cannot log in using my root password.
 
 Another thing is that Linux works perfect if I installed Fecore Core 7 on this multi-core machine with scsi/sata disk. Why it didnt work if I used re-compiled kernel. I guess it is because I didnt config kernel right (although I enabled all important features related with scsi/sata) in "make menuconfig". If you happen to know how to enable scsi/sata features correctly, please let me know. Thanks!
 
Below is my grub.conf related to 2.6.23 kernel. 
 
 
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/VolGroup00/LogVol00
#          initrd /initrd-version.img
#boot=/dev/sda
default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Fedora (2.6.20)
        root (hd0,0)
        kernel /vmlinuz-2.6.20 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
        initrd /initrd-2.6.20.img