Re: smp: am i seeing double?

[linux]

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" <[EMAIL PROTECTED]>
To: "linux" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
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
<[EMAIL PROTECTED]> 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).

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