Haswell GPU Architecture & Iris Pro

In 2010, Intel’s Clarkdale and Arrandale CPUs dropped the GMA (Graphics Media Accelerator) label from its integrated graphics. From that point on, all Intel graphics would be known as Intel HD graphics. With certain versions of Haswell, Intel once again parts ways with its old brand and introduces a new one, this time the change is much more significant.

Intel attempted to simplify the naming confusion with this slide:

While Sandy and Ivy Bridge featured two different GPU implementations (GT1 and GT2), Haswell adds a third (GT3).

Basically it boils down to this. Haswell GT1 is just called Intel HD Graphics, Haswell GT2 is HD 4200/4400/4600. Haswell GT3 at or below 1.1GHz is called HD 5000. Haswell GT3 capable of hitting 1.3GHz is called Iris 5100, and finally Haswell GT3e (GT3 + embedded DRAM) is called Iris Pro 5200.

The fundamental GPU architecture hasn’t changed much between Ivy Bridge and Haswell. There are some enhancements, but for the most part what we’re looking at here is a dramatic increase in the amount of die area allocated for graphics.

All GPU vendors have some fundamental building block they scale up/down to hit various performance/power/price targets. AMD calls theirs a Compute Unit, NVIDIA’s is known as an SMX, and Intel’s is called a sub-slice.

In Haswell, each graphics sub-slice features 10 EUs. Each EU is a dual-issue SIMD machine with two 4-wide vector ALUs:

Low Level Architecture Comparison
  AMD GCN Intel Gen7 Graphics NVIDIA Kepler
Building Block GCN Compute Unit Sub-Slice Kepler SMX
Shader Building Block 16-wide Vector SIMD 2 x 4-wide Vector SIMD 32-wide Vector SIMD
Smallest Implementation 4 SIMDs 10 SIMDs 6 SIMDs
Smallest Implementation (ALUs) 64 80 192

There are limitations as to what can be co-issued down each EU’s pair of pipes. Intel addressed many of the co-issue limitations last generation with Ivy Bridge, but there are still some that remain.

Architecturally, this makes Intel’s Gen7 graphics core a bit odd compared to AMD’s GCN and NVIDIA’s Kepler, both of which feature much wider SIMD arrays without any co-issue requirements. The smallest sub-slice in Haswell however delivers a competitive number of ALUs to AMD and NVIDIA implementations.

Intel had a decent building block with Ivy Bridge, but it chose not to scale it up as far as it would go. With Haswell that changes. In its highest performing configuration, Haswell implements four sub-slices or 40 EUs. Doing the math reveals a very competent looking part on paper:

Peak Theoretical GPU Performance
  Cores/EUs Peak FP ops per Core/EU Max GPU Frequency Peak GFLOPs
Intel Iris Pro 5100/5200 40 16 1300MHz 832 GFLOPS
Intel HD Graphics 5000 40 16 1100MHz 704 GFLOPS
NVIDIA GeForce GT 650M 384 2 900MHz 691.2 GFLOPS
Intel HD Graphics 4600 20 16 1350MHz 432 GFLOPS
Intel HD Graphics 4000 16 16 1150MHz 294.4 GFLOPS
Intel HD Graphics 3000 12 12 1350MHz 194.4 GFLOPS
Intel HD Graphics 2000 6 12 1350MHz 97.2 GFLOPS
Apple A6X 32 8 300MHz 76.8 GFLOPS

In its highest end configuration, Iris has more raw compute power than a GeForce GT 650M - and even more than a GeForce GT 750M. Now we’re comparing across architectures here so this won’t necessarily translate into a performance advantage in games, but the takeaway is that with HD 5000, Iris 5100 and Iris Pro 5200 Intel is finally walking the walk of a GPU company.

Peak theoretical performance falls off steeply as soon as you start looking at the GT2 and GT1 implementations. With 1/4 - 1/2 of the execution resources as the GT3 graphics implementation, and no corresponding increase in frequency to offset the loss the slower parts are substantially less capable. The good news is that Haswell GT2 (HD 4600) is at least more capable than Ivy Bridge GT2 (HD 4000).

Taking a step back and looking at the rest of the theoretical numbers gives us a more well rounded look at Intel’s graphics architectures :

Peak Theoretical GPU Performance
  Peak Pixel Fill Rate Peak Texel Rate Peak Polygon Rate Peak GFLOPs
Intel Iris Pro 5100/5200 10.4 GPixels/s 20.8 GTexels/s 650 MPolys/s 832 GFLOPS
Intel HD Graphics 5000 8.8 GPixels/s 17.6 GTexels/s 550 MPolys/s 704 GFLOPS
NVIDIA GeForce GT 650M 14.4 GPixels/s 28.8 GTexels/s 900 MPolys/s 691.2 GFLOPS
Intel HD Graphics 4600 5.4 GPixels/s 10.8 GTexels/s 675 MPolys/s 432 GFLOPS
AMD Radeon HD 7660D (Desktop Trinity, A10-5800K) 6.4 GPixels/s 19.2 GTexels/s 800 MPolys/s 614 GFLOPS
AMD Radeon HD 7660G (Mobile Trinity, A10-4600M) 3.97 GPixels/s 11.9 GTexels/s 496 MPolys/s 380 GFLOPS

Intel may have more raw compute, but NVIDIA invested more everywhere else in the pipeline. Triangle, texturing and pixel throughput capabilities are all higher on the 650M than on Iris Pro 5200. Compared to AMD's Trinity however, Intel has a big advantage.

The Prelude Crystalwell: Addressing the Memory Bandwidth Problem
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  • Old_Fogie_Late_Bloomer - Monday, June 03, 2013 - link

    The performance isn't earth-shattering, but if Intel manages to put out good open-source Linux drivers for Iris Pro, I can't help but feel like this would be a great chip for that; it isn't like you'll be playing Crysis in Ubuntu anytime soon. I kind of want that CRB (or something like it), actually. Reply
  • tviceman - Saturday, June 01, 2013 - link

    I'll bet notebooks with mid-range quad core CPU's and gt 750m discrete graphics will be cheaper than notebooks with Iris Pro enabled iGPU graphics as well. The only benefit would be a slightly slimmer chassis and battery life. Anyone who still wants to game on a notebook is noticeably better off with a mid-range discrete GPU over this. Reply
  • esterhasz - Saturday, June 01, 2013 - link

    On page four, the ominous launch partner is not "keen" rather than "key", I guess. I'd be very keen on having that rMBP 13" with IP5200, though. Reply
  • Ryan Smith - Saturday, June 01, 2013 - link

    Noted and fixed. Thank you. Reply
  • tipoo - Saturday, June 01, 2013 - link

    I'm very much in that boat too, a quad core 13" rMBP with Iris Pro would put it over the top. Reply
  • MattVincent - Wednesday, June 12, 2013 - link

    totally agree. I wonder if apple will actually put a quad core in the 13" though. I bet they would rather sell more 15" rmbp's Reply
  • jeffkibuule - Saturday, June 01, 2013 - link

    Would a 47W chip be able to fit into a normal 13" Ultrabook-like chassis like the 13" MacBook Pro with Retina Display? Only an extra 12W TDP to deal with. Reply
  • esterhasz - Saturday, June 01, 2013 - link

    This would be awesome and we have to remember that the 47W TDP includes voltage regulation moving off the MB, so the gap is maybe only 8W. The 47 TDP also refers to both CPU and GPU running at full speed, which is an extremely rare scenario - in gaming, the CPU load will probably hover at 50% only.

    In any case, if the tested model goes into a rMBP 13" I'm going to buy it before Tim Cook has left the stage.
    Reply
  • nofumble62 - Saturday, June 01, 2013 - link

    Thinking to buy a Ivybridge Mac Book Pro for my wife, I guess she will have wait a little longer for this baby. I wish they could fit in a Mac Book Air. Reply
  • jeffkibuule - Saturday, June 01, 2013 - link

    Look at the price of those chips though, you're going to be dropping at least $2000 on such a laptop when the CPU alone is $478. Reply

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