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RE: [Xen-users] Xeon 5160 vs 5080

To: "Nathan Allen Stratton" <nathan@xxxxxxxxxxxx>, "Christoph Purrucker" <cp+ml-xen@xxxxxxxx>
Subject: RE: [Xen-users] Xeon 5160 vs 5080
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Mon, 4 Sep 2006 15:35:12 +0200
Cc: xen-users@xxxxxxxxxxxxxxxxxxx, Javier Guerra <javier@xxxxxxxxxxx>
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Thread-topic: [Xen-users] Xeon 5160 vs 5080

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Nathan Allen Stratton
> Sent: 04 September 2006 14:29
> To: Christoph Purrucker
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx; Javier Guerra
> Subject: Re: [Xen-users] Xeon 5160 vs 5080
> On Mon, 4 Sep 2006, Christoph Purrucker wrote:
> > Nathan Allen Stratton wrote:
> >
> > > i have no clue why newer chips doesn't have it, neither 
> why AMD never
> > > bothered
> > > with something like that.  maybe there's some other 
> consideration i don't
> > > know about.
> >
> > The latter thing is quite simple: AMD threw the more 
> transistors of their
> > new production process in AMD64, the 64bit extension; Intel made HT
> > instead.
> Yet, there is some reason why Intel does not have it in the 51xx.

Put quite simply: Hyperthreading makes more sense on a very long
pipeline (because on any branch-mispredict or some other pipeline stall,
there is a second chance to have something useful to do, ready to run).
As I'm sure plenty of people are aware, Hyperthreading can give better
performance in some cases, but there are plenty of cases where it
actually performs worse. 

Since both the AMD processors and the newer Intel processors don't have
very long pipelines, they also haven't got Hyperthreading. 

Of course, everything in the processor design is a balance between the
performance gain and cost in transistors. 

> -Nathan
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