Intel's Sandy Bridge Architecture Exposed
by Anand Lal Shimpi on September 14, 2010 4:10 AM EST- Posted in
- CPUs
- Intel
- Sandy Bridge
New, More Aggressive Turbo
Lynnfield was the first Intel CPU to aggressively pursue the idea of dynamically increasing the core clock of active CPU cores while powering down idle cores. The idea is that if you have a 95W TDP for a quad-core CPU, but three of those four cores are idle, then you can increase the clock speed of the one active core until you hit that TDP limit.
In all current generation processors the assumption is that the CPU reaches that TDP immediately upon enabling turbo. In reality however, the CPU doesn’t heat up immediately - there’s a period of time where the CPU isn’t dissipating its full TDP - there’s a ramp.
Sandy Bridge takes advantage of this by allowing the PCU to turbo up active cores above TDP for short periods of time (up to 25 seconds). The PCU keeps track of available thermal budget while idle and spends it when CPU demand goes up. The longer the CPU remains idle, the more potential it has to ramp up above TDP later on. When a workload comes around, the CPU can turbo above its TDP and step down as the processor heats up, eventually settling down at its TDP.
While SNB can turbo up beyond its TDP, the PCU won’t allow the chip to exceed any reliability limits (similar to turbo today).
In addition to above-TDP-turbo, Sandy Bridge will also support more turbo bins than Nehalem/Westmere. Intel isn’t disclosing how much more turbo headroom we’ll have, but the additional bins are at least visible with multiple cores active. Current designs usually only turbo up one or two bins with all four cores active, I’d expect to see another bin or two there and possibly more in lighter load cases.
Both CPU and GPU turbo can work in tandem. Workloads that are more GPU bound running on SNB can result in the CPU cores clocking down and the GPU clocking up, while CPU bound tasks can drop the GPU frequency and increase CPU frequency.
Sandy Bridge as a whole is much more dynamic of a beast than anything that’s come before it.
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yuhong - Tuesday, September 14, 2010 - link
There is no VEX.256 for 256-bit integer ops, but there is a VEX.128 prefix that zeros the upper part of YMM registers to reduce the delays..NaN42 - Tuesday, September 14, 2010 - link
Well, I found a summary of the prefixes. Interestingly there are some exception, like I guessed, e.g. a VEX.128 prefix does not exist for conversion of packed floating points<->packed integers and for CRC32c + POPCNT.CSMR - Tuesday, September 14, 2010 - link
Anand:The best info available on an exciting platform, good job.
I wonder if for the next article you could test DirectX / OpenGL compatibility? Intel advertises compliance for a lot of its products, but in reality the support is partial, and some applications that use DirectX / OpenGL entirely correctly are not supported by Intel graphics, including the current HD graphics.
I've found this with fastpictureviewer (DirectX, I think 9) and Photoshop CS5 (OpenGL 2)
This is quite shocking. Given that Intel is doing this currently, it would be great if reviewers could prod it into action, but unfortunately they tend to place speed first, correctness second or nowhere.
marass31 - Thursday, September 16, 2010 - link
Hi CSMR,Could you please write more details about problems with DX and OGL on Intel HD graphics( including gfx driver version, system config ...). You mentioned about two applications: Fastpictureviewer and PSCS5, so could you please write some steps to reproduce to each of them - THX a lot.
ssj4Gogeta - Tuesday, September 14, 2010 - link
What's the point of extreme editions if we're going to have affordable K SKUs?Or will socket 2011 not have any K SKUs? I'm guessing they'll leave the BCLCK unlocked on the 2011, and only have normal and extreme processors (no K processors). Or maybe extreme editions will just have more cores like 980X?
DanNeely - Tuesday, September 14, 2010 - link
The extreme editions have always been for people who buy retail or who're playing with LN2 and need the most insanely binned part available. They've never been a mainstream OCer part.MonkeyPaw - Tuesday, September 14, 2010 - link
I have a bad feeling about the "k" chips and the future of overclocking. Sure, intel gave us turbo mode, but that almost seems like appeasement before the last shoe drops. First, limited turbo with good overclockng, then better turbo and less overclocking, and now it's sounding like slightly better turbo and even less overclocking. It looks like we are moving to intel-controlled overclocking. There's virtually no value left for the enthusiast--a user that is already just a small part of the market. Intel just decided what the enthusiast needs, but I don't think they get what those users actually want.I just don't buy that these limits are to prevent fraud. Mom and Pop stores are virtually all gone now, and I'd hate to think what Intel would do to a Dell or HP if they got caught overclocking desktops.
I guess this leaves another door open for AMD. Sad, cause SnB looks like a great design.
This Guy - Wednesday, September 15, 2010 - link
Hopefully Intel will allow the 'energy budget' to be increased when an extreme edition processer detects less thermal resistance (i.e. a bloody big heat sink). This would allow an EE CPU to either run with a higher multiplier or run at it's turbo frequency longer. (I'ld like this feature on all CPU's)This would make EE CPU's interesting if K CPU's catch up in terms of cores.
Shadowmaster625 - Tuesday, September 14, 2010 - link
What are the prospects for using Intel's transcoder to convert DVDs to 700MB avi files? Either DivX, Xvid, or H.264? Or anything else better than MPEG-2?Dfere - Tuesday, September 14, 2010 - link
Since this seems to be, overall, a refinement, and not so much an improvement with new capabilities, and Anand's comments about the scalability of GPU related enhancements, that Intel is taking a two step approach towards CPU releases, in addition to its fab strategies? E.G, we see a new CPU, then it gets shrunk, then it gets improved (like this), then it gets bells and whistles (like a GPU etc), then we start over again with a really new architecture.....