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

[Aleksandar Milivojevic]

Robert Hanson wrote:

> Are you saying that the standard stock CentOS 4 kernel does not recognize
> nor use or take advantage of HT on a stand alone Intel processor and
> motherboard? This is a 865PERL w/LAN I use for development and testing...

There are two "standard" kernels distributed with every Red Hat system 
(CentOS being clone of RHEL).  One without SMP support, and one with SMP 
support.  The reason is that SMP support adds additional overhead to the 
kernel (access to kernel structures must be locked, and so forth).  Most 
people are running UP machines, and therefore benefit from running 
kernel that is optimized for UP machines.

If you install CentOS on UP machine, Anaconda (that's the installer) 
will install only "kernel" package (the kernel optimized for UP 
machines, no SMP support).  If you install CentOS on SMP machine or on 
UP P4 HT machine, Anaconda will install both "kernel" and "kernel-smp" 
packages, and make SMP kernel default.

So, to answer you question.  Yes.  By default it will take advantage if 
you initally installed it on SMP machine.  If you installed on UP 
machine, and later on moved disks to SMP machine, you need to manually 
add kernel-smp package (not a big deal, rather trivial to do).

BTW, do note that HT processor still has only single core.  Some reports 
indicate that there's not much advantage of HT over non-HT processors 
(and consequently not much advantage of running SMP kernel on HT 
processor).  Your "two virtuall" processors are still running on single 
core.  The real thing (dual-core processors) is something Intel has 
announced to start shipping in near future.  Up until now, dual cores 
were limited to  RISC processors such as UltraSPARC and Alpha.

-- 
Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7