Re: Hyperthreading on 2.4.18 and 2.4.20 (Redhat)

From: General Schvantzkoph (
Date: 03/18/04

Date: Wed, 17 Mar 2004 21:38:12 -0500

On Wed, 17 Mar 2004 22:56:25 +0000, red floyd wrote:

> I have an RH8 box, with 2 P4 Xeons. I recently enabled hyperthreading
> in the BIOS, but am still only seeing 2 CPUs.
> I have tried Redhat kernels 2.4.18-14 and 2.4.20-28.8. I looked at the
> source in arch/i386/kernel/{setup,smpboot}.c, and it looks like there's
> an error in the hyperthreading detection logic. There's some major
> changes to this code in the vanilla 2.4.25 kernel.
> Anyone got HT working on an SMP box with a stock RH kernel?
> Alternatively, what's the diff between a RH kernel and a vanilla kernel?
> If I put a vanilla kernel on this box, will it break any RH specific stuff?
> Thanks in advance

A standard kernel will work fine, go ahead and build a 2.4.25 and give it
a try. BTW hyperthreading doesn't work very well, my tests showed that
hyperthreading increades throughput by only 10% while reducing individual
thread performance by 25%.