ARM’s Mali Midgard Architecture Explored
by Ryan Smith on July 3, 2014 11:00 AM ESTMidgard: The Modern Mali
As ARM’s current-generation SoC GPU architecture, at the highest level the Midgard architecture is an interesting take on GPUs that in some ways looks a lot like other GPUs we’ve seen before, and in other ways (owing to its uncommon ancestry) is radically unlike other GPUs. This is coupled with the fact that as an SoC GPU supplier, ARM is in an interesting position where they can offer both CPU and GPU designs to 3rd party licensees, unlike most other GPU designers who either use their designs internally (Qualcomm, NVIDIA) or only license out GPUs and not ARM CPUs (Imagination). From a sales perspective this means ARM can offer the CPU and GPU designs together in a bundle, but perhaps more importantly it means they have the capability design the two in concert with each other, being in the position of the sole creator of the ARM ISA.
Architecturally Midgard is a direct descendant of Utgard. While there is a significant difference in how unified and discrete shaders operate, and as a result they cannot simply be swapped, the resulting shader design for Midgard still ends inheriting many of Utgard’s design elements, features, and quirks. At the same time the surrounding functionality blocks that compose the rest of the GPU have received their own upgrades over the years to improve performance and features, but are none the less distinctly descended from Utgard as well. At the end of the day this is a distinction more important for programmers than it is users (or even tech enthusiasts), but going forward it’s interesting to note just how similar Utgard and Midgard are, a similarity we don’t normally see between unified and discrete shader designs.
From a design standpoint Midgard is designed to span much of the range for SoC GPUs, from cheap, area-efficient designs to relatively massive designs with an eye on gaming. In doing so ARM offers a few different variations on the Midgard design that are all architecturally identical, but will vary slightly in features and internal organization. So for the purposes of today’s article we’ll be focusing on ARM’s latest and greatest design, Mali-T760, but we will also be calling out differences as necessary.
First and foremost then, let’s talk about design goals and features. Unlike the bare bones OpenGL ES 2.0 Utgard architecture, Midgard has been designed to be a more feature-rich architecture that not only offers solid graphics performance but solid compute performance too. This is in part a logical extension of what a unified shader GPU can already do – they’re innately good at mass math for graphics, so compute is only a minor stretch – but also a deliberate decision by ARM to push compute harder than they would otherwise have to for merely a graphics product.
From an API standpoint then Midgard was designed as what is best described as an OpenGL ES 3.0+ part. The architecture was designed from the start to offer functionality beyond what OpenGL ES 3.0 would offer, a decision that has since benefitted ARM by allowing Midgard parts to keep up with newer API standards. In fact ARM has just recently completed OpenGL ES 3.1 conformance testing, with their updated drivers passing Khronos’s required tests. As such all Midgard parts at a hardware level can support OpenGL ES 3.1, with software support reliant on OS and device vendors shipping updated OSes and drivers that enable 3.1 functionality.
Even then Midgard has some functionality that has gone untapped, but will be enabled in the Android ecosystem through the upcoming Android Extension Pack for Android L. The AEP will further build off of OpenGL ES 3.1 by enabling features such as tessellation and geometry shaders, features that did not make it in to 3.1. As with OpenGL ES 3.1, ARM has confirmed that they expect all Midgard GPUs to support the AEP.
Finally, along with OpenGL ES support, ARM also officially offers Direct3D support on Midgard. This functionality has not yet been tapped – all Windows Phone and Windows RT devices so far have been Qualcomm or NVIDIA based – but in principle it is there. One thing to note however is that among the Mali 700 series, only Mali-T760 is Direct3D Feature Level 11_1 capable. Mali-T720 however only supports level 9_3, more befitting of the market realities and its status as a lower cost, lower complexity part.
Meanwhile from a compute standpoint Midgard is intended to be a strong competitor by supporting Android’s RenderScript framework and OpenCL 1.2 full profile. OpenCL support on SoC GPUs has been spotty due in part to the fact that the major OSes haven’t consistently supported it (iOS never has and Android only recently), and of those SoC GPUs that do support it, not all of them support the full profile as opposed to the much more restricted embedded profile. As is often the case with GPU computing just how well this functionality is used is up to the capabilities and imaginations of developers, but ARM has made it clear that they’re fully backing GPU computing even in the SoC space.
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darkich - Friday, July 4, 2014 - link
You guys are missing the fact that Snapdragon 805 can reach a much higher memory bandwidth than Tegra K1.TheJian - Saturday, July 5, 2014 - link
But it still loses to K1 in most gpu stuff (all?). You're forgetting AMD/NV have had 20yrs of trying to figure out how to get the most they can from bandwidth for gaming. The devs have had that long working with their hardware also (game devs I mean). Everyone else has to play catch up here for years as they've never had to do anything game wise until last year or so as android etc gaming pumped up a bit.That is why you see ZERO Qcom optimized games (or did I miss one?) :) It's easier to optimize for a chip you already know inside out (amd/nv). I even went to Qcom's gaming page just to see if there were any games they had on their list that were REQUIRING snapdragon to see xx effects etc. There were none last I checked. All the games are just on googleplay with no snapdragon mention (like on NV games they say THD, and these games look quite a bit better than the regular versions) as they appear to work on ALL players chips. Google seems to be realizing K1 is where you want to be on gpu's at least for gaming centric stuff/automotive and I'd expect devs to continue to favor NV for optimizations as they don't need to learn a thing about k1 it's KEPLER which they've already spent 2yrs+ playing with (probably longer as they get dev versions long before we get a retail card so games can be made/optimized for them by the time they hit).
At 20nm xbox360/ps3 will be left behind as new games keep getting made on mobile. If you're not on xbox1/ps4 you'll be buying some cheap 20nm console box that has cheap games ($2-20 vs. $60 for xbox1/ps4) and as good or better graphics than last gen xbox360/ps3. GDC 2013 & 2014 surveys show devs are already massively making games for mobile and as 20nm kicks in everyone has K1 power levels or more. These android consoles/tv's etc will have more tricks than those ancient consoles so you should be able to get much better gaming experience on them for $100-200. The games pricing alone is a draw for poor people. With the ports happening right an left now of quality PC/console games and super cheap pricing there is even more reason to run to mobile for poor people who never played them before (half-life2, trine2, Serious Sam3BFE, none sold more than 11mil or so). There are a billion android users and most clearly have played none of this stuff even the console ports like Final Fantasy games, GTA games etc (on or off PC also doesn't matter) haven't been played by more than 10mil or so combined each. Lost of great stuff for poor people to pick up for under $10 in ports until the REAL new games for mobile hit this xmas/next xmas. All of the stuff the dev surveys show they've been working on will hit this year or next, and they are not angry birds games.
przemo_li - Tuesday, July 8, 2014 - link
Alternative view on Google stance:Nvidia is just first vendor that allowed them to show more features than are possible on Apples A7.
(Mobile-only vendors are not interested in full OpenGL...)
TheJian - Sunday, July 6, 2014 - link
If they're worried about lawsuits (odd they'd say that without merit), they must have had their lawyers tell them they'd be sued due to stealing tech that is probably from AMD/NV. DMCA takedowns, completely closing the kimono so to speak shows they are afraid for good reason. It isn't just competitor crap as nobody else is afraid of that it seems. The same tricks are being used by almost everyone to a large degree. So it seems to me they clearly owe someone some money and don't want to pay. They will probably show their details once they remove that stuff from a future gen soc or never I guess if they just can't remove it for some reason :)mczak - Thursday, July 3, 2014 - link
You could add Intel HD graphics (baytrail) though. Also quite interesting architecture-wise imho.btw some small correction wavefront size for amd (gcn) is 64, not 16 (I think this was wrong on older anandtech articles too). The simd size is 16 indeed but the same instruction is executed for 4 clocks always (on 16 different elements of the wavefront each clock).
mczak - Thursday, July 3, 2014 - link
Here's actually an explanation how the wavefront size of 64 works for gcn:http://devgurus.amd.com/thread/168154
Achtung_BG - Thursday, July 3, 2014 - link
My first touch phone is black LG Viewty in 2008 with Mali GPU :) :) :) If you have new article for android extention pack comparison with full Open GL will be very intrasting.Jedibeeftrix - Thursday, July 3, 2014 - link
yes please.i'd like to know:
1. how long until the AEP is rolled back into what will be OpenGL ES 4.0
1.1. whether it represents a subset of an existing OpenGL full-fat version (eg 4.4)
2. how this compares to DX 11.2 feature wise
2.1. whether AEP will be expanded in OpenGL ES 4.0 to make it broadly DX 11.2 compliant
przemo_li - Tuesday, July 8, 2014 - link
1) Never. (Though, separate extensions, can get into ES. AEP is just thin bundle over many other extensions)1.1) Yes. OpenGL 4.x is still capable of running AEP code.
2) DX11.2 is single vendor en-devour currently... (And You really should compare to F(eature)L(evel)11_2).
2.1) WHY?
Why on earth You need all those things?
Industry move in different direction. (Mantle, DX12, Metal, AZDO)
Doing stuff efficiently is new mantra now.
Adding more stuff from DX FL11_2 (Yes if You talk about features You MUST use F(eature)L(evels)!!!), would only complicate things for OpenGL ES.
We need AZDO.
Kevin G - Thursday, July 3, 2014 - link
I can see Qualcomm's concerns about a shader arms race in mobile: it has already happened on the CPU side without much benefit to the consumer. However, with the explosion in screen resolution in tablets, a spec race here would have a more tangible benefit for consumers. It sitll boggles my mind that a retina iPad has 50% more pixels and a slower GPU than my desktop system with a 1080p monitor driven by a GTX 770. My sole concern would be temperatures and power consumption.Well if Qualcomm isn't going to disclose the information, how much can be implied from driver information? Qualcomm purchased the mobile Radeon drivision from AMD back in 2009 and then came up with the anagram Adreno. If they're still using a design based upon what they got form AMD, it'd be reflective in similar drivers. If they've come up with a new architecture, it too would be evident in radically different drivers. The details would be lacking of course but some generalities could be made.