NVIDIA Tegra 4 Architecture Deep Dive, Plus Tegra 4i, Icera i500 & Phoenix Hands On
by Anand Lal Shimpi & Brian Klug on February 24, 2013 3:00 PM ESTRound Two, Still Quad-Core
I have to give NVIDIA credit, back when it introduced Tegra 3 I assumed its 4+1 architecture was surely a gimmick and to be very short lived. I remember asking NVIDIA’s Phil Carmack point blank at MWC 2012 whether or not NVIDIA would standardize on four cores for future SoCs. While I expected a typical PR response, Phil surprised me with an astounding yes. NVIDIA was committed to quad-core designs going forward. I still didn’t believe it, but here we are in 2013 with NVIDIA’s high-end and mainstream roadmaps both exclusively featuring quad-core SoCs. NVIDIA remained true to its word, and the more I think about it, the more the approach makes sense.
In the PC industry we learned that there’s no real downside to quad-core as long as you can power gate individual cores, and turbo up to higher frequencies when fewer than four cores are active, there’s no real tradeoff other than cost. You get good multithreaded performance when you need it, and single threaded performance doesn’t suffer. Tegra 3 complicated things because it was on an older, more power hungry process when Qualcomm introduced its first Krait parts. Tegra 4 on the other hand comes to market on the absolute latest and greatest 28nm HPL process from TSMC. And like Tegra 3, each Cortex A15 core in Tegra 4 can be independently power gated.
Like most of the evolution in the mobile space, NVIDIA skipped the silly transitional period between dual and many core and just ended up exactly where it knows the story ends. Heavily threaded apps are still rare on mobile OSes, but with each core independently power gated the user shouldn’t pay a penalty for them being there as long as NVIDIA and the device vendor don’t configure the DFVS tables improperly.
The downside is cost, not to the end user, but to NVIDIA. Economically, NVIDIA was able to make Tegra 3 work for itself with a die size somewhere around 80mm^2. The move to 28nm allowed NVIDIA to increase transistor count, without straying from that die size. Tegra 4 is a bit larger than Tegra 3, but it’s still somewhere in that 80mm^2 range.
Wafer costs for 28nm HPL are undoubtedly higher than 40nm LPG at TSMC, not to mention any differences in yield between T3 and T4, so without a doubt Tegra 4 will cost NVIDIA more than Tegra 3. All of that being said however, NVIDIA still seems to take a conservative approach to die sizes in mobile, which gives it the flexibility to significantly undercut Qualcomm in costs to OEMs. I do believe this was a key part of NVIDIA’s success last year with Tegra 3 ending up in both the Nexus 7 and Microsoft’s Surface RT. Long term, simply selling your SoCs for less than the competition isn’t a path to market dominance, but being able to do so helps buy NVIDIA time while it gathers the remaining missing pieces of the mobile platform (integrated baseband, RF front end, WiFi, etc...). Tegra 4 isn’t the sort of drive the industry forward type of silicon we’re used to seeing from NVIDIA, but it’s sized appropriately given NVIDIA’s position in the market. From a business standpoint, NVIDIA is making the right decisions to ensure the Tegra business at least has a chance of succeeding.
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xsacha - Saturday, March 23, 2013 - link
Tegra4i uses Cortex-A9. Krait is similar to Cortex-A15. The Krait obviously uses way more power and gives way more performance clock-for-clock. So you are comparing apples and oranges here. The 1.9GHz Krait quad-core is roughly equivalent to 2.5GHz+ in a Tegra 4i.name99 - Monday, February 25, 2013 - link
"But in favor of quad-core: software might start using cores a little more effectively w/time--Google and Apple are apparently trying to make WebKit able to do things like HTML parsing and JavaScript garbage collection in the background, and Microsoft's browser team backgrounds JavaScript compilation"It would be wise to design for the technology we have today, not the dream of technology we may one day have. As I have stated elsewhere, there is ample evidence that on the desktop, even today, multiple threads running on more than two cores at once is very rare. (More precisely
- many apps are multithreaded, but those threads tend to be mostly async IO type threads, mostly waiting
- there is a mild win to having three cores available, but it's not much advantage over two cores
- the situation has improved a little over ten years ago (when the first SMT P4s first started appearing) and when there was little advantage to two cores over one. But most of the improvement is the result of OS vendors moving as much stuff as possible of what they do (GUI, IO, etc) onto the second core.)
The only real code that utilizes multiple cores is video-encoding. In particular both games and photo processing do not use nearly as much multi-core as people imagine.
The situation for mobile is the same, only a little worse because there is less of simultaneous heavyweight apps running.
Given these facts, and the way code is actually structured today, 4 cores makes very little sense.
SMT makes sense, mainly in that its power and area footprint is very low, so it's a win on those occasions when the OS can make use of it. Beyond that, if you have excess transistors available, beefed up vectors (wider registers, and wider units) probably makes more sense. You'll notice that these recommendations parallel what Intel has done over the past few years --- they are not idiots, and desktop code is very similar to mobile code.
As for parallel web browsing, people have been publishing about it for years now; but the real world results remain unimpressive. It remains an unfortunate fact that the things that have been converted to parallel don't seem to be, for most sites, the things that are actually gating performance. A similar problem exists with PDF display (still not as snappy as I would like on an iPad3) --- the simple and obvious things you can imagine for parallelizing the rendering aren't the things that are usually the problem.
In both cases, the ideal situation would be to restart with totally redesigned file formats that are non-serial in nature; but that seems to be a "boil-the-ocean" strategy that no-one wants to commit to yet. (Though it would be nice if Apple and Adobe could get together to redefine a PDF2.0 file format that was explicitly parallel, and that seems rather easier than fixing the web.)
Krysto - Sunday, February 24, 2013 - link
It seems Nvidia really pulled off making Tegra 4's GPU 6x faster than Tegra 3, and with 5 Cortex A15 cores and 6x more GPU cores, all in the same size. Pretty impressive. But still quite disappointing for lack of OpenGL ES 3.0 and OpenCL support. I really hope they plan on supporting them in Tegra 5 along with the new 64 CPU and Maxwell-based GPU cores.Mike1111 - Sunday, February 24, 2013 - link
I would really like to see an analysis/comparison of companion core (Nvidia) vs. big.LITTLE (Samsung).lmcd - Sunday, February 24, 2013 - link
BIG.little (fixed it for ARM) isn't even in reference device stage yet is it?Krysto - Monday, February 25, 2013 - link
No need to fix it. The "opposite" style naming is intentional. It's ironic. Get it?phoenix_rizzen - Monday, February 25, 2013 - link
Exynos 5 Octa, which is A15/A7 big.LITTLE, has been demoed. Tegra 4, which is A15 plus a companion core, has been demoed.Neither are commercially available, neither are in shipping products, neither are available to consumers.
IOW, the Cortex-A15 variations for bit.LITTLE have passed the reference stage, and are in the "find companies to use them to build devices" stage. They'll be in consumers' grubby little hands before Christmas 2013.
tviceman - Sunday, February 24, 2013 - link
GPU performance ended up better than I thought it would after the subdued announcement and leaked early prototype benchmarks. Good to see.wongwarren - Monday, February 25, 2013 - link
I wonder which is faster. This or the Snapdragon 600.varad - Monday, February 25, 2013 - link
Snapdragon 600:http://www.anandtech.com/show/6792/lg-optimus-g-pr...
Tegra 4:
http://www.anandtech.com/show/6787/nvidia-tegra-4-...
So if the metric is simply raw performance [since you asked "faster"], looks like the Tegra 4 will win easily against the Snapdragon 600.
A better/fair comparison would be when we have performance numbers for Snapdragon 600 in a tablet or Tegra 4 in a phone.