The iPhone 6 Review
by Joshua Ho, Brandon Chester, Chris Heinonen & Ryan Smith on September 30, 2014 8:01 AM EST- Posted in
- Smartphones
- Apple
- Mobile
- iPhone 6
A8’s GPU: Imagination Technologies’ PowerVR GX6450
Last but not least on our tour of the A8 SoC is Apple’s GPU of choice, Imagination’s PowerVR GX6450.
When Apple first announced the A8 SoC as part of their iPhone keynote, they told us to expect a nearly 50% increase in graphics performance. Based on that information and on the fact that that Apple was moving to a denser 20nm process, we initially believed that Apple would be upgrading from A7’s 4-core PowerVR design to a 6-core design, especially in light of the higher resolution displays present on the iPhone 6 and iPhone 6 Plus.
Instead our analysis with Chipworks found that only four GPU cores were present on A8, which ruled out the idea of a 6-core design but did narrow down the options considerably. Based on that information and more importantly Apple’s Metal Programming Guide, we have been able to narrow down our options to a single GPU, the PowerVR GX6450.
The GX6450 is the immediate successor to the G6430 first used in the A7 and is based on Imagination’s PowerVR Series6XT architecture. Imagination first announced PowerVR Series6XT to the public at CES 2014, and now just a short eight months later we are seeing the first Series6XT hardware reach retail.
We have already covered the PowerVR Series6/Series6XT architecture in some detail earlier this year so we won’t go through all of it again, but we would encourage anyone who is interested to take a look at our architectural analysis for additional information. Otherwise we will be spending the bulk of our time looking at how GX6450 differs from G6430 and why Apple would choose this specific GPU.
From a technical perspective Series6XT is a direct evolution over the previous Series6, and GX6450 is a direct evolution over G6430 as well. Given a 4-core configuration there are only a limited number of scenarios where GX6450 outright has more hardware than G6430 (e.g. additional ALUs), and instead Series6XT is focused on adding features and improving performance over Series6 through various tweaks and optimizations to the architecture. Series6 at this point is actually over two years old – it was first introduced to the public at CES 2012 – so a lot has happened in the mobile GPU landscape over the past couple of years.
The closest thing to a marquee feature on Series6XT is support for Adaptive Scalable Texture Compression (ASTC), a next-generation texture compression technology that is slowly making its way into GPUs from a number of manufacturers. Designed by the consortium responsible for OpenGL ES, Khronos, ASTC is designed to offer better texture compression (with finer grained quality options) than existing texture compression formats while also being a universal format supported by all GPUs. In Apple’s case they have always been using PowerVR GPUs – and hence all products support PVRTC and more recently PVRTC2 – however ASTC being exposed allows them to take advantage of the quality improvements while also making game development and porting from other platforms easier.
Less visible to users but certainly important to Apple, Series6XT also includes new power management capabilities to reduce power consumption under idle and light workloads. Through finer grained power gating technology that Imagination dubs “PowerGearing G6XT”, GX6450 can now have its shading clusters (USCs) powered down individually, allowing only as many of them as are necessary to be fired up. As Apple continues to min-max their designs, being able to idle at a lower power state can be used to improve battery life and/or increase how often and how long the A8’s GPU uses higher power states, improving overall efficiency.
Apple iPhone GPU Performance Estimate: Over The Years
And, perhaps most importantly overall, Series6XT comprises a series of under-the-hood optimizations to improve overall performance. When it comes to the internals of PowerVR architectures we only have limited details from Imagination on how they operate, so in some areas we know quite a bit about what Imagination has been up to and in other areas their architectures are still something akin to a black box. At any rate Imagination’s goal for Series6XT was to improve performance by up to 50% – this seems to be where Apple’s 50% performance improvement claim comes from – though as we’ll see the performance gains on real world applications are not going to be quite as potent.
What we do know about Series6XT is that Imagination has made some changes to the structure of the USCs themselves. Series6XT still uses a 16-wide SIMD design, but in each pipeline they have added another set of medium/half-precision (FP16) ALUs specifically to improve FP16 performance. Now instead of 2x3 (6) FP16 ALUs, Series6XT bumps that up to 4x2 (8) FP16 ALUs. This is the only outright increase in shader hardware when you compare Series6 to Series6XT, and on paper it improves FP16 performance by 33% at equivalent clock speeds.
The focus on FP16 is interesting, though for iOS it may be misplaced. These half-precision floating point operations are an excellent way to conserve bandwidth and power by not firing up more expensive FP32 ALUs, but the tradeoff is that the numbers they work with aren’t nearly as precise, hence their use has to be carefully planned. In practice what you will find is that while FP16 operations do see some use, they are by no means the predominant type of floating point GPU operation used, so the FP16 increase is a 33% increase only in the cases where performance is being constrained by the GPU’s FP16 performance.
FP32 performance meanwhile remains unchanged. Each USC pipeline contains two such ALUs, for up to four FP32 FLOPS per clock, or to use our typical metric, 128 MADs (Multiply-Adds) per clock.
The rest of Series6XT’s optimizations take place at the front and back ends, where geometry processing and pixel fill take place respectively. Imagination has not told us exactly what they have done here, but both these areas have been targeted to improve sustained polygon rates and pixel fillrate performance. These more generic optimizations stand to be more applicable to general performance, though by how much we cannot say.
One final optimization we want to point out for Series6XT is that Imagination has made some additional under-the-hood changes to improve GPU compute performance. We have not talked about GPU compute on iOS devices thus far, as until now Apple has not exposed any APIs suitable for it (e.g. OpenCL is not available on iOS). With iOS8 Apple is releasing their Metal API, which is robust enough to be used for both graphics and now compute. How developers put this capability to use remains to be seen, but GX6450 should perform even better than G6430.
| Mobile SoC GPU Comparison | ||||||||||
| PowerVR SGX 543MP2 | PowerVR SGX 543MP3 | PowerVR SGX 543MP4 | PowerVR SGX 554MP4 | PowerVR G6430 | PowerVR GX6450 | |||||
| Used In | iPad 2/iPhone 4S | iPhone 5 | iPad 3 | iPad 4 | iPad Air/iPhone 5s | iPhone 6/iPhone 6Plus | ||||
| SIMD Name | USSE2 | USSE2 | USSE2 | USSE2 | USC | USC | ||||
| # of SIMDs | 8 | 12 | 16 | 32 | 4 | 4 | ||||
| MADs per SIMD | 4 | 4 | 4 | 4 | 32 | 32 | ||||
| Total MADs | 32 | 48 | 64 | 128 | 128 | 128 | ||||
| GFLOPS @ 300MHz | 19.2 GFLOPS | 28.8 GFLOPS | 38.4 GFLOPS | 76.8 GFLOPS | 76.8 GFLOPS | 76.8 GFLOPS | ||||
| Pixels/Clock | N/A | N/A | N/A | N/A | 8 | 8 | ||||
| Texels/Clock | N/A | N/A | N/A | N/A | 8 | 8 | ||||
The one wildcard when talking about performance here is going to be clock speeds. Apple doesn’t expose these and they aren’t easy to test for (yet), though in the long term Metal offers some interesting possibilities for nailing that down, or at least getting a better idea of relative clock speeds.
In any case, we’ll take a look at our GPU benchmarks in depth in a bit, but overall GPU performance compared to A7 and its G6430 is consistently better, but the exact performance gain will depend on the test at hand. Some tests will come very close to reaching 50% while others will be just 15-20%. The dependent factor generally seems to be whether the test is ALU-bound or not; because the USC has not changed significantly from G6430 to GX6450 outside of those additional FP16 ALUs, tests that hit the FP32 ALUs in particular show less of an improvement. Otherwise more balanced tests (or at least tests more defined by pixel fillrate performance) can show greater gains. In general we should be looking at a 30-35% performance improvement.
Why Four Cores?
One thing that admittedly surprised us in the revelation that A8 was using a 4-core PowerVR design was that we figured a 6-core design would be a shoe-in for A8, especially since Apple was on the receiving end of the density improvements from TSMC’s 20nm process. But upon further reflection an additional two cores is likely more than Apple needed nor wanted.
The biggest factor here is that coming from G6430 in the A7, performance has seen a solid improvement despite sticking to only four GPU cores. Due to the combination of performance improvements from the Series6XT architecture and any clock speed increases from Apple, A8 gets quite a bit more GPU performance to play with. The increased resolution of the iPhone 6 screen in turn requires more performance if Apple wants to keep native resolution performance from significantly regressing, which GX6450 is capable of delivering on. Never mind the fact that G6430 also drove the iPad Air and its much larger 2048x1536 pixel display.
| PowerVR Series6/6XT "Rogue" | ||||||||||||
| GPU | # of Clusters | # of FP32 Ops per Cluster | Total FP32 Ops | Optimization | ||||||||
| G6200 | 2 | 64 | 128 | Area | ||||||||
| G6230 | 2 | 64 | 128 | Performance | ||||||||
| GX6240 | 2 | 64 | 128 | Area | ||||||||
| GX6250 | 2 | 64 | 128 | Performance | ||||||||
| G6400 | 4 | 64 | 256 | Area | ||||||||
| G6430 | 4 | 64 | 256 | Performance | ||||||||
| GX6450 | 4 | 64 | 256 | Performance | ||||||||
| G6630 | 6 | 64 | 384 | Performance | ||||||||
| GX6650 | 6 | 64 | 384 | Performance | ||||||||
These performance improvements in Series6XT have a cost as well, and that cost is suitably reflected in the estimated die sizes for each GPU. The G6430 was 22.1mm2 on the 28nm A7, while the GX6450 is 19.1mm2 on A8. Though GX6450 is smaller overall, it’s nowhere near the roughly 11.1mm2 a pure and perfect die shrink of G6430 would occupy. Limited area scaling aside, GX6450’s additional functionality and additional performance requires more transistors, and at the end of the day Apple doesn’t see a significantly smaller GPU because of this. In other words, the upgrade from G6430 to GX6450 has delivered much of the performance (and consumed much of the die space) we initially expected to be allocated to a 6-core GPU.
Overall the choice of GX6450 seems to be one of picking the GPU best for a phone, which is an area the G6430 proved effective with A7. As a step below Imagination’s 6-core PowerVR designs, GX6450 delivers a better balance between performance and power than a larger GPU would, which in turn is clearly a benefit to Apple. On the other hand this means A8 is not going to have the GPU performance to compete with the fastest SoCs specifically designed for tablets, though what this could mean for the obligatory iPad update remains to be seen.
Facebook
Twitter
RSS
531 Comments
View All Comments
annah_souls - Tuesday, October 28, 2014 - link
Yes, it's my money and I have a lot of them to buy as much as iPhone as I like. If you don't satisfy Apple product, you may not but $2000 handbag also. Pity you to yell Apple "The world is not fair!" LOLDonkey2008 - Wednesday, October 29, 2014 - link
People with intelligence don't buy purely on specs, which it seems 100% of Android owners do. I can just picture you like the many Android fanboys I have met....."Deeeerp, it has foure cores witch iz twice as mony as en iPhone so itz twice as fast, Deeeerrp".Enjoy your clunky, resource-hog, half-baked Google OS, your extremely inefficient hot-and-crispy quad-core space heater SOC (which has to be throttled by Android so the phone doesn't melt LULZ) and premium plastic-wrapped junk.
leonhk1 - Wednesday, October 29, 2014 - link
Hi,I have stock of Brand New Apple iPhone 6 - 64GB Unlocked phones for sale at $650 only, sealed in box with 1 year warranty. Available in Gold , silver and space grey colors
Interested buyer should E-mail me at: megas83@yahoo.co.uk
iphone 3 - Friday, October 31, 2014 - link
I am wondering if you guys have similar analysis for ipad air 2 A8xodedia - Tuesday, November 4, 2014 - link
Please check the NAND differences between the 64gb model and the 128gb model. It appears the 128gb model uses TLC and not MLC.curiosity - Thursday, November 6, 2014 - link
output power / voltage: per channel or combined?sellcheapli - Monday, November 24, 2014 - link
Apple iPhone 6 - Plus 4G 16GB , 64GB , 128GB (Grey,Silver,Gold) ... $600sellcheapli - Monday, November 24, 2014 - link
Apple iPhone 6 - Plus 4G 16GB , 64GB , 128GB (Grey,Silver,Gold) ... $600Apple iPhone 6 - 16GB , 64GB , 128GB (Grey,Silver,Gold) ... $500
Message : sellcheaplimited@gmail.com
Apple_iPhone_Service - Thursday, April 30, 2015 - link
http://www.iphoneservicecenterchennai.coFind the best Iphone Service center in your area in Chennai & Bangalore
iphone service center in Anna Nagar | iphone service center in Mogappair | iphone service center in Thirumangalam | iphone service center in Perambur | iphone service center in Egmore | iphone service center in Kilpauk | iphone service center in Aminjikarai | iphone service center in Koyambedu | iphone service center in Kodambakkam | iphone service center in Nungambakkam | iphone service center in TNagar | iphone service center in Royepettah | iphone service center in Mylapore | iphone service center in Teynampet | iphone service center in Saidapet | iphone service center in Guindy | iphone service center in Ashok Nagar | iphone service center in KK Nagar | iphone service center in Saligramam | iphone service center in Virugambakkam | iphone service center in Chrompet | iphone service center in Pallavaram | iphone service center in Tambaram | iphone service center in Velachery | iphone service center in Thiruvanmiyur | iphone service center in Adyar | iphone service center in OMR | iphone service center in ECR | iphone service center in Medavakkam | iphone service center in Madipakkam | iphone service center in Perumbakkam | iphone service center in Pallikaranai | iphone service center in Sholinganallur | iphone service center in Gopalapuram | iphone service center in Besant Nagar | iphone service center in Washermenpet | iphone service center in Broadway | iphone service center in Purusawalkam
iphone service center in koramangala | iphone service center in jayanagar | iphone service center in jp nagar|iphone service center in btm | iphone service center in ulsoor | iphone service center in kammanahali | iphone service center in cox town \ iphone service center in frazer town | iphone service center in mathikere | iPhone Service Center in kempapura | iphone service center in marathalli | iphone service center in hsr | iphone service center in electronic city | iphone service center in sg playa | iphone service center in Bellandur | iphone service center in Domlur | iphone service center in Malleswaram | iphone service center in Rajajinagar | iphone service center in majestic | iphone service center in forum mall | iphone service center in Sony world signal | iphone service center in echo space | iphone service center in forum mall | iphone service center in Whitefield
We provide wide-range of Hardware & Software services for all branded smartphones and tablets including brands like APPLE, SAMSUNG, HTC, SONY, LG, MOTOROLA, MICROMAX, LENOVO etc. can recover the smartphone devices from any sort of problems like physical damage, Water lock and replacing the core components like Display , IC's, Front and Rear Camera components and other hardware/software issues.
Training
Topics Discus under Training Program:
Soldering, De-soldering of components, Check of voltages in a battery of a mobile phone, Use of SMD reworks station, Triggering of batteries, Assembling & disassembling of mobile phones, Chip level servicing of components: Power amplifiers (pf), audio IC (Cobba), CPU (Mad), Power supply IC (Cont), Charging Control IC (Chaps). Rf Signal Processor IC (Hagar). Also well versed with SMD components replacement (Capacitors, Diodes Resistors, and LED’s). Rebelling & repair of ball grade array ICs (BGA).
Hardware Complaint Service Training:
Mobile Complaints: Dead, network, display problem, keypad problem, display light problem, keypad light problem, touchpad problem, sensor problem, head phone jack problem, speaker problem, mic problem, ringer problem, charging problem, Bluetooth problem, wifi problem, camera problem, volume button problem, camera button problem, on off switch problem, strip problem, fm problem, network problem, dead, water lock, hanging problem, handset off problem, restart issue
Software Complaint Service Training:
Phone unlock, pattern lock, vibrator problem, navigation key problem, Contact service, hanging, partial dead, network, unlocking, Flashing various software like USR, twister, tornado, griffin, UFS, Uni Box for color, camera, blue tooth, infrared enabled mobile phones of Nokia, Samsung, Panasonic, Ericson, Sony, Siemens, LG, Motorola and many more
Motherboard Complaint Service Training:
Ic (integrated circuit), Smd ic (leg type), bga ic (ball type)capacitor, Resister ,transistor, filter, fuse, diode, power crystal, clock crystal connector, battery connector ,usb jack, charging jack, head phone chack, inner key pad, vibrator ,speaker, mic, ringer
Koramangala 5th block
no 75/8,kristal prestige 4th floor, idea show room upstairs,opp to bhima jewellers,
koramangala industrial layout, 5th block, 7026604420/ 7026604423
Koramangala 7th block
no 340, maruthi plaza,1st b cross,koramangala 7th block
opp to forum road,behind A2B, 08041521112
Koramangala 1st Block
no 16,vijith plaza,80ft road,koramangala 1st block
opp to reliance fresh, 08041521115
jayanagar 4th block
Diamond Arcade,no 21,east 11th main,32nd d cross,jayanagar 4th block
opp to kalamandir & mom and me,near cool joint signal
08041521113
jayanagar 9th block
no 1339,41st cross,25th main,jayanagar 9th block
opp to central mall road,behind jain college,next to himalaya store
08041521110/
Banashankari 1st stage
no 5,Sln complex,80 ft road,srinivasa nagar circle,banashankari 1st stage
near bata showroom
08041521119
Banashankari 2nd stage
no31, 21st main road, near bda complex,banashankari 2nd stage
near goli vada pav
08049570768 / 9980090798
Rajajinagar 6th block
no 246,Dr.Rajkumar Road,Rajajinagar 6th block
next to nea albek hotel & sangeetha mobile showroom
08041521116
Malleswaram
no 10,2nd main,sampige main road.near mantri mall,
opp to albek hotel,below to samsung show room
malleswaram, 08041474313
Mathikere
28/3, Sai Shekar complex,H.M.T Main Road, Beside Subbaiah Hospital
08041573366 / 9611269682
Kempapura
Door no-3, 21st main road, sri Rajeshwari New Colony, Hebbal,
Kempapura Main Road, Bangalore
08042103355 / 9611269682
ulsoor
no 49&50, guru gowtham complex,SV road,next to metro station,
below to manak jewellers , ulsoor, 08041520642
Domlur
no 11,service road,old airport road,next to hyundai showroom,befor sony show room
domlur in towards mg road, 08041103602
Frazer town
no 64/1, concord plaza, coles road, frazer town, near shanthi sagar hotel
08041105150
Kammanahalli
no 17,mathu mansion,kammanahalli circle near,opp to ganesha temple
below to liberty showroom, 08041103592
BTM
no 746,Tayapa towers,13th main,7th cross,near udupi garden,opp to dominas,icici,peter england
below to mumbai kitchen , 08041500208
HSR
no 2580, 27th main, 13th cross,next to PHD
08049530063
Bellandur
No 71/1a,opp to swarnamukhi hospital,univercell upster,sarjapura main road
next to bellandur total mall, 08042060460
Jp Nagar 7th Phase
no 243, Brigate Apartment signal opposite, jp nagar 7th phase
08040958575
Marathahalli
No: 35/1B, CRM SOWBHAGYA ANNEXE, Shop No.2,Varthur Main Road,
marathahalli bridge next,Munnekolala,
08065304422,09043888404
VV puram
Anna nagar
no 18, TNSCB shopping complex,near jsp honda showroom,
thirumangalam junction water tank,anna nagar west,
04430069841
Velachery
no 25,sambantham garden,100ft road tharamani link road,opp to karaikudi hotel near TCS
velachery, 04442139797
OMR(thoraipakkam)
no 64/4, sri vidhya avenue,omr ptc main road,opp to kfc restaurant
04465668880
Anna nagar-2
Muva’s arcade,C52/4,anna nagar east,near chinthamani roundana circle, opp to girias
chennai-600102
04449539191
T-Nagar
No 2 ,North usman Road,Kodambakkam Road Junction ,Near Motherhood T-nagar,
below Mallika mansion Chennai-17
04443527474
apple iphone service center in abu dhabi
apple iphone service center in abu dhabi
iphone service center in abu dhabi
apple iphone service center in dubai
apple iphone authorized service center in dubai
apple iphone authorised service centre in dubai
apple iphone service center in dubai
apple iphone authorized service center in dubai
apple iphone authorised service centre in dubai
apple iphone authorized service center in dubai
apple iphone authorised service centre in dubai
iphone service center in bur dubai
iphone service center in deira dubai
iphone service dubai
iphone service dubai
iphone service center dubai
iphone service in dubai
apple iphone service center uae
apple iphone service centre uae
apple iphone service center uae
apple iphone service centre uae
apple iphone service center dubai
apple iphone service center in uae
apple iphone service centre in uae
raj parihar - Tuesday, November 3, 2015 - link
mcf doesn't have any Multiply operations. In A8, its benefiting from a better (tuned) prefetcher possibly with negative (-3 or -1) stride.