Re: smp: am i seeing double?

["linux" <linux@networkingnewsletter.org.uk>]

Yes, I'd clicked it was HT. I've had a quick trawl of web pages but not come up 
with any "make sure you turn HT off" issues so I'm going to leave it on for now. 
Time permitting I might play around and see if/how HT affects the running of my 
main codes (MPI processing of atmospheric physics/chemistry models). Cheers! 
Michael
----- Original Message ----- 
From: "Jens Bech Madsen" <jbmadsen@gmail.com>
To: "linux" <linux@networkingnewsletter.org.uk>
Cc: <debian-user@lists.debian.org>
Sent: Friday, November 12, 2004 6:01 PM
Subject: Re: smp: am i seeing double?


> On Fri, 12 Nov 2004 17:14:28 -0000, linux
> <linux@networkingnewsletter.org.uk> wrote:
> > A quick question about hardware. I'm 99% sure my box has 2 Xeon processors in
> > it. I had installed the sarge kernel then got the
> >     kernel-image-2.4.27-1-686-smp_2.4.27-1.backports.org.1_i386.deb
> > package and installed smoothly using `dpkg -i <kernel-image... .deb>`, 
> > rebooted
> > into that kernel. I now seem to be seeing 4 (four!) processors eg as reported 
> > by
> > `top`, `cat /proc/cpulist` and in the /var/log/messages file. (Aside: with 
> > the
> > uni-processor kernel, `top` only reported 1Gb memory but the smp kernel,
> > correctly, reports the 2Gb memory
> >
> > I've just rebooted to WinXP and the SystemProperties implies there's 2
> > processors on the 'General' tab, but lists 4 on the
> > Hardware->DeviceManager->Processors tab and indeed the TaskManager also 
> > implies
> > there's 4 CPUs.
> >
> > Any ideas what's going on?
>
> It's because of hyperthreading. Each processor appears like two to the
> OS. You can most likely change it in your BIOS if you think your OS
> performs better with two CPU's instead of four (there are cases this
> might be true).