The Sandy Bridge Preview
by Anand Lal Shimpi on August 27, 2010 2:38 PM ESTA New Architecture
This is a first. Usually when we go into these performance previews we’re aware of the architecture we’re reviewing, all we’re missing are the intimate details of how well it performs. This was the case for Conroe, Nehalem and Lynnfield (we sat Westmere out until final hardware was ready). Sandy Bridge, is a different story entirely.
Here’s what we do know.
Sandy Bridge is a 32nm CPU with an on-die GPU. While Clarkdale/Arrandale have a 45nm GPU on package, Sandy Bridge moves the GPU transistors on die. Not only is the GPU on die but it shares the L3 cache of the CPU.
There are two different GPU configurations, referred to internally as 1 core or 2 cores. A single GPU core in this case refers to 6 EUs, Intel’s graphics processor equivalent (NVIDIA would call them CUDA cores). Sandy Bridge will be offered in configurations with 6 or 12 EUs.
While the numbers may not sound like much, the Sandy Bridge GPU is significantly redesigned compared to what’s out currently. Intel already announced a ~2x performance improvement compared to Clarkdale/Arrandale, and I can say that after testing Sandy Bridge Intel has been able to achieve at least that.
Both the CPU and GPU on SB will be able to turbo independently of one another. If you’re playing a game that uses more GPU than CPU, the CPU may run at stock speed (or lower) and the GPU can use the additional thermal headroom to clock up. The same applies in reverse if you’re running something computationally intensive.
On the CPU side little is known about the execution pipeline. Sandy Bridge enables support for AVX instructions, just like Bulldozer. The CPU will also have dedicated hardware video transcoding hardware to fend off advances by GPUs in the transcoding space.
Caches remain mostly unchanged. The L1 cache is still 64KB (32KB instruction + 32KB data) and the L2 is still a low latency 256KB. I measured both as still 4 and 10 cycles respectively. The L3 cache has changed however.
Only the Core i7 2600 has an 8MB L3 cache, the 2400, 2500 and 2600 have a 6MB L3 and the 2100 has a 3MB L3. The L3 size should matter more with Sandy Bridge due to the fact that it’s shared by the GPU in those cases where the integrated graphics is active. I am a bit puzzled why Intel strayed from the steadfast 2MB L3 per core Nehalem’s lead architect wanted to commit to. I guess I’ll find out more from him at IDF :)
The other change appears to either be L3 cache latency or prefetcher aggressiveness, or both. Although most third party tools don’t accurately measure L3 latency they can usually give you a rough idea of latency changes between similar architectures. In this case I turned to cachemem which reported Sandy Bridge’s L3 latency as 26 cycles, down from ~35 in Lynnfield (Lynnfield’s actual L3 latency is 42 clocks).
As I mentioned before, I’m not sure whether this is the result of a lower latency L3 cache or more aggressive prefetchers, or both. I had limited time with the system and was unfortunately unable to do much more.
And that’s about it. I can fit everything I know about Sandy Bridge onto a single page and even then it’s not telling us much. We’ll certainly find out more at IDF next month. What I will say is this: Sandy Bridge is not a minor update. As you’ll soon see, the performance improvements the CPU will offer across the board will make most anyone want to upgrade.
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DrRap - Friday, August 27, 2010 - link
It's Anand "intel" lal Shimpi.Anand Lal Shimpi - Friday, August 27, 2010 - link
I agree that single threaded performance is important to keep in mind. Sandy Bridge had a larger ILP boost than I expected. Final silicon with turbo enabled should address that even more.We got into trouble chasing the ILP train for years. At this point both AMD and Intel are focused on thread level parallelism. I'm not sure that we'll see significant ILP gains from either party for quite a while now.
The socket move is silly, unfortunately there's nothing that can be done about that. AMD takes better care of its existing board owners, that's something we've pointed out in prior reviews (e.g. our Phenom II X6 review).
I'm not sure I'd call Sandy Bridge a kiddie chip however. It looks like it'll deliver great bang for your buck when it launches in Q1 regardless of how threaded your workload is.
Value scatterplots are a great idea, Scott does a wonderful job with them. We're going to eventually integrate pricing data with Bench (www.anandtech.com/bench) which should help you as well :)
Take care,
Anand
ssj4Gogeta - Saturday, August 28, 2010 - link
I'm guessing USB 3.0 support will be introduced later with a chipset upgrade. Why are you so concerned with GHz when Sandy Bridge delivers more IPC? I think having better IPC instead of more GHz is better as you'll get potentially lower power consumption.asmoma - Friday, August 27, 2010 - link
Lets just hope AMD trhows in 80 gpu cores into ontario to bring this SB igp to shame(almost the same performance but less than 10w tdp). And lets also hope they throw in those 400 cores into Llano we have been hearing about.mfago - Friday, August 27, 2010 - link
Any news on OpenCL support? I image Apple may hold off on a purely integrated GPU unless that is supported.Thanks!
Anand Lal Shimpi - Friday, August 27, 2010 - link
Sandy Bridge's GPU does not support OpenCL. This is strictly a graphics play, Intel doesn't have an announced GPU compute strategy outside of what it's doing with Larrabee.Take care,
Anand
DanNeely - Friday, August 27, 2010 - link
Is intel actually still doing anything with Larrabee on the gfx side? I thought they killed it on that end entirely and were looking at it strictly as a compute platform now.Anand Lal Shimpi - Saturday, August 28, 2010 - link
Correct - as of today the only Larrabee parts are for the HPC market. Didn't mean to confuse there :)Take care,
Anand
JonnyDough - Friday, August 27, 2010 - link
"Correction, you'll be able to buy it next year, but you'll get to meet her today."Sandy could be a boy too!
JonnyDough - Friday, August 27, 2010 - link
By the way, is it a an it, or a girl? You can't have it both ways!