We are using CentOS-4.3 (x86_64) with Opteron servers, and noticed a problem with cpuspeed:
If we reboot by doing "# reboot" or similar from a shell, the boot will hang not long after cpuspeed starts. The machine freezes: ctrl-alt-del doesn't work, and only pressing the reset button or a power cycle will restart the machine.
If we reboot from power-up or by pressing the reset button, there is no hang, and the boot proceeds normally.
Another strange thing is that only some boxes have this problem. Others, seemingly identical, reboot just fine. We've compared the BIOS settings, the CPU steppings, etc., and they seem to be identical. It's very odd. Maybe we're missing a BIOS setting, but we couldn't find a difference.
We've fixed this just by turning off the cpuspeed service.
It took some trial and error to figure out this was caused by cpuspeed. Misleadingly, the hang doesn't occur immediately after "Starting cpuspeed: [OK]" prints. Instead it occurs when trying to bring up a network interface, which is almost right after cpuspeed starting. With the original 2.6.9-34.ELsmp, it's at "Bringing up interface eth0". With the 2.6.9-34.0.2.ELsmp (and all other rpms updated), it hangs at "Bringing up loopback interface". This may just be a timing thing.
We can just forget about cpuspeed, but if any of you have any advice, we'd appreciate it. Otherwise I am basically posting this to save diagnostic time for those who encounter these symptoms in the future.
These are dual-core dual Opteron 265/270 servers with Tyan K8SD Pro motherboards.
Thanks, Dan