The Agility to Move Your Business Forward. Hmm. Hmmmmmmm. If I'd had seen that marketing slogan say three years ago, when Xeon had zero competition for enterprise-class x86-based computing, there'd be less scepticism in my words. But when it sits as the premier slogan when you hit up the Intel Xeon sub-site, given the current nemesis they face, my mind starts to doubt.

You know the story by now: AMD released the Opteron over two years ago in September 2003, as the first example of the company's new K8 core, a core that debuted the AMD AMD64/x86-64 microprocessor architecture. Opteron slapped Xeon around back then, and it's done so ever since. The basic architecture behind that first Opteron then made it to the desktop, and the same story played out there, too.

With Opteron ruling a significant roost since release, large scores of massive enterprises, small businesses, academia and the scientific world - and probably everyone in between to boot - runs infrastructure, datacentres and processing behemoths on the chips that have made AMD the most famous in their history.

These days it's all about Intel trying to kick back at - if you'll permit me the horrible (but funny for an article on CPUs) mental image - the pair of AMD swinging testes that represent enterprise and desktop. In short, Intel would dearly love to hoof AMD in those balls. It's just a bit of a shame that all recent signs point to that only happening when Merom, Conroe and Woodcrest are released. Those chips use a brand new microarchitecture, the 8th generation of CPU technology from Intel, that replaces the current 7th-generation NetBurst.

Until that new architecture puts its boots on and takes careful aim, Intel is still waving its silicon willy around with NetBurst-based processors. To its credit, though, Netburst can be a bit of a big one. Recent times have seen it paired up with larger on-chip caches, faster frequencies, decent stabs at power saving technology (some of the Netburst family have certainly needed it!) and, of course, dual cores.

We've had a look at dual-core Intel processors on HEXUS in 2005, starting with the Intel Pentium Extreme Edition 840 and most recently the Pentium D 820, with both based on Netburst performance tenets.

Now it's Xeon's turn to do the dual-core Netburst dance. Paxville is the name of the core, and it's that which has to do another gruelling 12 rounds with Opteron until Woodcrest takes the tag and wrestles whatever AMD have around by then.

The next page does all the explaining about Paxville and platform specifics, so join me in the HEXUS evaluation of the last Xeon DP chip architecture, before Intel get rid of the current stuff and start fresh in 2006 with something new.

While it would take a case-by-case analysis to exhaustively prove the Xeon's current shortcomings, even a cursory educated guess will get you close. It's the basics of the platform that trip it up, with the sharing of limited resources among too many consumers that have it languishing some distance behind current SMP dual-core Opteron. Having a single DDR2-400 memory controller, and all the latency-increasing, bandwidth-decreasing things that says to you, versus a good desktop DDR2 solution for dual-core Intel, is one of the larger drawbacks. The requirement for registered memory is correct for the audience and places Paxville DP will operate, and Paxville MP even more so, but the fact is that Opteron's on-CPU memory controller more effectively hides the extra latency from registered memory.

Less than 4GiB/sec to share between the better-performing four cores is pretty measly, with each Opteron core enjoying roughly twice that with interleaved accesses to a shared MC on 2-way dual-core Opteron. Downstream from the MCH, if you want to do any I/O, there's not much of a link to the ICH5R, itself really old, and only the PCI-X segment bridge gets any real bandwidth deserving of a high-end workstation system.

Turning on HT on the Paxville system just made things even worse. HyperThreading creates two processors for the OS to schedule threads on, per core, but remember that core is singular. There's still the same dual-ALU, dual-issue, long-stage pipeline to share. Cache misses, pipeline stalls and other facets that stall performance on a single-threaded core, hurt up to twice as much on a HyperThreaded system. Make all those CPUs fight for access to lacking resources such as the memory controller and I/O ASICs and you have a recipe for something that's not going to go very fast in the majority of situations.

Opteron simply does things much better, with an infrastructure and topology better suited to memory access and I/O, with HyperTransport links aplenty in modern multi-way Opteron systems for pretty much anything you can think of. It's basic CPU architecture, with a 14-stage, dual-issue (ADD and MUL per cycle) main integer pipeline, that scales to within 400MHz of the 31-stage Netburst core in Paxville, means it'll really just crap all over that core in terms of basic CPU-bound performance.

The only real situation where the 8-way Paxville DP setup will have nice performance win versus anything else in two sockets, is if all eight threads come from the same HT-aware app that's doing a nice, easy blend of integer math, that sits completely inside the 2MiB of L2 per core. Ideally, with Paxville's L1 cache being so low latency, you want it all running inside of the 16KiB L1 cache space, but you'd be lucky. You don't want to do I/O, and you don't want to touch the MCH, really. It'd be just as well.

Ah well! Intel have been bumbling around with Xeon for ages, and this latest evolution brings nothing but larger L2, dual-core and trouble with HT on, for the most part. Outside of something like a webserver serving static content, or a contrived scientific application, I'm struggling to see the appeal in any way.

Paxville DP at 2.8GHz is $1030 or so in quantity at the time of writing, making them $300 or so cheaper than the Opteron 280s that trounced them in this article. For the beating Opteron dishes out, the price difference of ~30% is just about right. That is until you consider the 200MHz slower Opteron 275 at $1050, which would knock the Paxville out in much the same manner, meaning this judge is scoring it a no-contest. It makes the discussion about the Opteron 280 also being cooler and quieter, and therefore easier to live with as a workstation, moot.

We wait for Woodcrest, then.