question about Intel P4 versus Alpha's

Daniel Kidger Daniel.Kidger at
Thu Jan 9 04:57:18 PST 2003

Not quite true - the giveaway about hyperthreads is if 'top' shows twice as
many lines starting with 'CPU' than you have real cpu's. (You can get the
same info from /proc/cpuinfo).

In general, people prefer to switch off hyperthreading for HPC clusters,
either via a BIOS option, or by passing 'noht' to the kernel (in say

I think that it was the P4 Xeon Prestonia that was the first that had
hyperthreading. It started at 1.8GHz


Dr. Dan Kidger, Quadrics Ltd.      daniel.kidger at
One Bridewell St., Bristol, BS1 2AA, UK         0117 915 5505
----------------------- --------------------

-----Original Message-----
From: Henderson, TL Todd [mailto:Todd_Henderson at]
Sent: 08 January 2003 19:49
To: 'Patrick Geoffray'
Cc: 'beowulf at'
Subject: RE: question about Intel P4 versus Alpha's

These are P4 2.4 ghz and I didn't find anything in the bios about it.  I
thought I had read on Intel's website that hyperthreading was only in the
3.xx ghz P4's?


-----Original Message-----
From: Patrick Geoffray [mailto:patrick at]
Sent: Wednesday, January 08, 2003 1:38 PM
To: Henderson, TL Todd
Cc: 'beowulf at'
Subject: Re: question about Intel P4 versus Alpha's

Hi Todd,

On Wed, 2003-01-08 at 10:49, Henderson, TL Todd wrote:
> 95-100%cpu utilization range.  However, now we have a cluster of P4's and
> when I look at top, it is more like 70-80% cpu usage.  This is using the
> same number of cpu's, the same switch, same code, and same problem for the
> code.  The jobs are still completing in about 30-40% less time, so we are
> getting a speed up.

Is Hyper-threading enabled ?


Patrick Geoffray, Phd
Myricom, Inc.
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