[CentOS] CentOS 4 and Intel P4 without Hyper-Threading vs. IntelP4 with Hyper-Threading

Wed Apr 20 23:17:43 UTC 2005
John Newbigin <jnewbigin at ict.swin.edu.au>

Robert Hanson wrote:

> ... and that if I upgrade to a SMP kernel on this machine that I will have
> no problem on a single processor machine/motherboard and HT will then be
> enabled?
> I "seem to" recall posts on this list recently where people were "disabling"
> HT on their multi-processor Intel boxen because of problems.

For the most part, it is safe to run the UP or the SMP kernel on any 
machine with or without HT and/or multiple CPUs.

In some rare cases, one kernel or the other will not work as expected 
(ie. at all) and you might have to supply some boot parameters like 
noacpi etc.  If you do have a problem though, just reboot into the other 

Other people have summarised HT.  If you can afford to test it (on a 
live system) turn it off in the BIOS to be safe (or ignore it and use 
the UP kernel).

If you do have multiple CPUs or a yet to be released dual core CPU then 
you probably want to use the SMP kernel or you have hardware sitting idle.

Some poorly written drivers don't like SMP.  Everything that comes 
standard with CentOS should be SMP safe but if you start adding 3rd part 
drivers, watch out.


John Newbigin
Computer Systems Officer
Faculty of Information and Communication Technologies
Swinburne University of Technology
Melbourne, Australia