I needed to install CentOS 6 on one an old Acer Aspire One notebook (with Intel Atom CPU) for some software testing. The problem is, that it could not perform a reboot, and I needed to press the power button every time. These instructions for reboot=X parameter for kernel did not help at all.
What really helped, is `kernel-ml` package from elrepo.org repositories. At the moment of writing, it was version `4.0.0-1.el6.elrepo.x86_64`.
Keep in mind that after installing kernnel-ml package, you need to edit /etc/grub.conf and make this new kernel as default. No additional boot options are required.