Barcelona Architecture: AMD on the Counterattack
by Anand Lal Shimpi on March 1, 2007 12:05 AM EST- Posted in
- CPUs
Introduction
Over the past several years, Intel has followed an odd path of microprocessor design. On the heels of the success of the P6 core, Intel set two teams in motion - one to work on the NetBurst architecture that would be the foundation of the Pentium 4, and one to work on a low-cost, low power highly integrated core that would eventually be redesigned into the Pentium M. The team eventually charged with designing the Pentium M took a more evolutionary approach building off of the strengths of the P6 architecture, while the NetBurst team preferred a radical departure from Intel's previously most successful architecture at the time.
We all know how this story ends; as NetBurst evolved, so did the underlying architecture of the Pentium M. Dothan was the first tweak of the Pentium M and it was mostly a clean up job to fix some performance issues with the original core. Higher clock speeds, more cache, and slight increases in IPC were on Dothan's CV.
Intel's Israel Development Center (IDC) then took Dothan and re-architected it to be a native dual core solution, complete with a shared L2 cache, the first of its type for an Intel processor. The Dothan to Yonah progression was far more significant than the move from Banias to Dothan, not just because Yonah was dual core but also because of the many architectural improvements that went into Yonah.
The next step Intel took is one we're all familiar with, and involves the most radical design change of the Pentium M's short lived history; Intel took Yonah and made it wider, deeper, and far more efficient. Out came the Core 2 line of processors and with it, Intel regained the undisputed performance crown it hadn't seen ever since the debut of AMD's Athlon 64.
While many argued that Banias, the first Pentium M core, was merely a modern take on the P6 architecture it's hard to see much in common between today's Core 2 and the 11 year old Pentium Pro. The P6 core was a starting point for a long line of evolution that brought Intel to where it is today.
AMD took a far more conservative approach over the past several years; it all started with the success of the K7 core, effectively a wider, faster, competitor to later versions of Intel's P6 architecture. While one of Intel's teams was busy making radical departures from anything AMD or Intel had done in the past, AMD didn't have the luxury of running two large scale microprocessor projects in tandem. The solution was to take the K7 core and improve on it, rather than taking a risky step in a different direction.
The K8 core was born as an evolution of the K7; with a slightly deeper pipeline, slight architectural improvements and an integrated Northbridge, the K8 was a pretty major evolutionary step for AMD over the K7. In fact, it took the Core 2 Duo to truly outperform the K8 core across the board, although Dothan and Yonah came quite close in certain applications.
AMD had worked on dramatic successors to the K8, rumored to be K9 and K10, but both appeared to be scrapped or at least focus was shifted away from them in favor of a more evolutionary take on the K8 architecture. The main difference here that allowed Intel to catch up to AMD's performance is that while Intel's Pentium 4 team was operating on the usual schedule of a 5-year micro-architecture cycle, the Pentium M team at IDC was updating its architecture every year. Banias, Dothan, Yonah and Merom/Conroe all happened in a period of four years, and during that same time AMD's K8 remained unchanged.
If Intel had continued down the Pentium 4/NetBurst route, sticking to the usual 5-year design cycle would have probably worked just fine for AMD but Intel had the luxury of having two major micro-processor teams working in parallel, one of which had a much better idea. Luckily it would seem that AMD realized it needed to compete with Intel using smaller evolutionary steps every couple of years rather than leaving an architecture relatively untouched for 4 - 5 years and thus the Barcelona project was created. Although it's set to debut around a year after Intel's Core 2 Duo that swiped the performance crown, Barcelona is AMD's best chance at remaining competitive.
Barcelona's window of opportunity is slim, depending mostly on how Intel's transition to 45nm goes. Publicly Intel has stated that its architectural update to Core 2, codenamed Penryn, will begin shipping by the end of 2007. However, current roadmaps show availability at sometime in 2008 with no word on when significant quantities will be available. Should Intel take longer than expected with the move to its 45nm Penryn core, Barcelona's mid-2007 launch on servers and Q3 '07 launch for desktops may come at a relatively quiet time for Intel.
Over the past several years, Intel has followed an odd path of microprocessor design. On the heels of the success of the P6 core, Intel set two teams in motion - one to work on the NetBurst architecture that would be the foundation of the Pentium 4, and one to work on a low-cost, low power highly integrated core that would eventually be redesigned into the Pentium M. The team eventually charged with designing the Pentium M took a more evolutionary approach building off of the strengths of the P6 architecture, while the NetBurst team preferred a radical departure from Intel's previously most successful architecture at the time.
We all know how this story ends; as NetBurst evolved, so did the underlying architecture of the Pentium M. Dothan was the first tweak of the Pentium M and it was mostly a clean up job to fix some performance issues with the original core. Higher clock speeds, more cache, and slight increases in IPC were on Dothan's CV.
Intel's Israel Development Center (IDC) then took Dothan and re-architected it to be a native dual core solution, complete with a shared L2 cache, the first of its type for an Intel processor. The Dothan to Yonah progression was far more significant than the move from Banias to Dothan, not just because Yonah was dual core but also because of the many architectural improvements that went into Yonah.
The next step Intel took is one we're all familiar with, and involves the most radical design change of the Pentium M's short lived history; Intel took Yonah and made it wider, deeper, and far more efficient. Out came the Core 2 line of processors and with it, Intel regained the undisputed performance crown it hadn't seen ever since the debut of AMD's Athlon 64.
While many argued that Banias, the first Pentium M core, was merely a modern take on the P6 architecture it's hard to see much in common between today's Core 2 and the 11 year old Pentium Pro. The P6 core was a starting point for a long line of evolution that brought Intel to where it is today.
AMD took a far more conservative approach over the past several years; it all started with the success of the K7 core, effectively a wider, faster, competitor to later versions of Intel's P6 architecture. While one of Intel's teams was busy making radical departures from anything AMD or Intel had done in the past, AMD didn't have the luxury of running two large scale microprocessor projects in tandem. The solution was to take the K7 core and improve on it, rather than taking a risky step in a different direction.
The K8 core was born as an evolution of the K7; with a slightly deeper pipeline, slight architectural improvements and an integrated Northbridge, the K8 was a pretty major evolutionary step for AMD over the K7. In fact, it took the Core 2 Duo to truly outperform the K8 core across the board, although Dothan and Yonah came quite close in certain applications.
AMD had worked on dramatic successors to the K8, rumored to be K9 and K10, but both appeared to be scrapped or at least focus was shifted away from them in favor of a more evolutionary take on the K8 architecture. The main difference here that allowed Intel to catch up to AMD's performance is that while Intel's Pentium 4 team was operating on the usual schedule of a 5-year micro-architecture cycle, the Pentium M team at IDC was updating its architecture every year. Banias, Dothan, Yonah and Merom/Conroe all happened in a period of four years, and during that same time AMD's K8 remained unchanged.
If Intel had continued down the Pentium 4/NetBurst route, sticking to the usual 5-year design cycle would have probably worked just fine for AMD but Intel had the luxury of having two major micro-processor teams working in parallel, one of which had a much better idea. Luckily it would seem that AMD realized it needed to compete with Intel using smaller evolutionary steps every couple of years rather than leaving an architecture relatively untouched for 4 - 5 years and thus the Barcelona project was created. Although it's set to debut around a year after Intel's Core 2 Duo that swiped the performance crown, Barcelona is AMD's best chance at remaining competitive.
Barcelona's window of opportunity is slim, depending mostly on how Intel's transition to 45nm goes. Publicly Intel has stated that its architectural update to Core 2, codenamed Penryn, will begin shipping by the end of 2007. However, current roadmaps show availability at sometime in 2008 with no word on when significant quantities will be available. Should Intel take longer than expected with the move to its 45nm Penryn core, Barcelona's mid-2007 launch on servers and Q3 '07 launch for desktops may come at a relatively quiet time for Intel.
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JustKidding - Friday, March 2, 2007 - link
So what you are saying is that it's not the size of your cache that matters as much as how well you use it.VooDooAddict - Thursday, March 1, 2007 - link
With Cache size differences usually having small impact on performance for Athlon64s, the slight trade off for better yields and margins seems the better choice for AMD here.
Regs - Thursday, March 1, 2007 - link
Where was this article 8 months ago? ;)I agree with Anands closing article that AMD now needs it's own "snowball effect" for the next couple of years. 4-5 years with a sitting target against a giant like Intel prooved to be costly in terms of competivness.
We all saw it coming when Intel developed the first Pentium M. It looks like AMD got the message as well and started the Barcelona project. Maybe AMD learned their lesson.
iwodo - Thursday, March 1, 2007 - link
So bascially all intel 's C2D improvement are made into Barcelona. And apart from Virtualization improvement there are nothing new from AMD that Intel doesn't have?On performance note Barcelona doesn't seem to offer better clock scaling. I.e even if it is 30% faster then its current K8 it will only have slight advantage against C2D clock per clock. Not to mention it is up against Penryn. Although Penryn is nothing much then a few minor tweaks and more cache. It does allow intel to scale higher in clock speed.
And given AMD slow roll out rate, and AMD limited production capacity Barcelona never seem like much of a threat.
The article does not mention anything about FP improvement. Are AMD keeping them secret for now or is that all we are going to see?
Spoelie - Thursday, March 1, 2007 - link
The FP improvement is the SSE improvement, and according to the theory it's more powerful than what core2 duo is offering.There are improvements mentioned that are not in core2 (+ other way around, like instruction fusing), and improvements that are inspired on the same principle but implemented differently. The architectures themselves differ widely (see earlier article that compares K8 with Core2 - reservation station etc.) so different implementations of principally the same optimizations on a different architecture will have vastly different effects. Even after these improvements, the capabilities (how much can you decode, etc) of each read nothing alike. And if it were all the same, AMD has the platform advantage, so it would still end up faster by virtue of nothing else but that. Some guesstimates made by varying sites would put Barcelona ahead in FP code and at the same level or slightly behind in INT code. But those are just guesstimates.
What I'm trying to say here is that barcelona is still very different from core2, and that we just don't know yet in which direction the pendulum will swing ;)
Shintai - Thursday, March 1, 2007 - link
No....precisely in theory is where Barcelona lacks. Core 2 Duo could in theory do 6 64bit or 3 128bit SSE instructions per cycle. Barcelona can do 4 64bit or 2 128bit. AMD provided this information aswell.Griswold - Thursday, March 1, 2007 - link
Wishful thinking.Spoelie - Thursday, March 1, 2007 - link
Hmmm, in the earlier article, there was explicit emphasis on the fact that 2 of the 3 units are symmetric in core2, but I'm not too sure what it means. It does imply however that those 3 units of core2 can only be used fully in certain combinations, and are not 3 independent units. On 128-bit performance, what was said is this: "so the Core architecture has essentially at least 2 times the processing power here [compared to K8]". Not 3 times, but "at least" 2 times, so again the 3 times will probably only be in certain situations.The next paragraph said this:
"With 64-bit FP, Core can do 4 Double Precision FP calculations per cycle, while the *Athlon64* can do 3."
So K8 was not at such a big disadvantage when it came to 64-bit SSE, if Barcelona doubles everything SSE, it should come ahead in this area.
So to me it looks like for 128-bit, core2 will be faster in some situations, on par in others, and for 64-bit, Barcelona would be ahead.
If this is wrong, I do not know where some of the articles I read over time came from, implying Barcelona would be better overall in SSE.
Shintai - Friday, March 2, 2007 - link
Core 2 got 3 individual SSE ports:http://www.realworldtech.com/page.cfm?ArticleID=RW...">http://www.realworldtech.com/page.cfm?ArticleID=RW...
AMD says 4 double:
http://www.anandtech.com/showdoc.aspx?i=2768&p...">http://www.anandtech.com/showdoc.aspx?i=2768&p...
And 64 or 128bit doesnt matter. I dont know how you think that way.
Barcelona got 2 SSE ports. They are able to do 2 128bit or 4 64bit. Most 128bit actually contains 2 64bit or 4 32bit.
Core 2 got 3 SSE ports. They are able to do 3 128bit or 6 64bit.
flyck - Friday, March 2, 2007 - link
core duo has 3 SSE units but they are not symmetric, meaning that not every unit can execute all commands. Core duo can do at best 4DP flops/ cycle. the same as barcelona.