GPU Performance - Great GPU, So-So Thermals Designs

The GPUs on the A15 iPhones are interesting, this is the first time that Apple has functionally segmented the GPU configurations on their SoCs within the iPhone device range, with the iPhone 13 mini and iPhone 13 receiving a 4-core GPU, similar to the A14 devices last year, while the 13 Pro and 13 Pro Max receive a 5-core variant of the SoC. It’s still the same SoC and silicon chip in both cases, just that Apple is disabling one GPU core on the non-Pro models, possibly for yield reasons?

Apple’s performance figures for the GPU were also a bit intriguing in that there weren’t any generational comparisons, just a “+30%” and “+50%” figure against the competition. I initially theorized to mean +10% and +28% against the A14, so let’s see if that pans out:

3DMark Wild Life Unlimited

In the 3DMark Wild Life test, we see the 5-core A15 leap the A15 by +30%, while the 4-core showcases a +14% improvement, so quite close to what we predicted. The peak performance here is essentially double that of the nearest competitor, so Apple is likely low-balling things again.

In terms of sustained performance, the new chips continue to showcase a large difference in what they achieve with a cold phone versus a heated phone, interestingly, the 4-core iPhone 13 lands a bit ahead of the 13 Pro here, more on this later.

Basemark GPU 1.2 - Medium 1440p - Off-Screen / Blit

In Basemark GPU, the 13 Pro lands in at +28% over the 12 Pro, with the 4-core iPhone 13 only being slightly slower. Again, the phones throttle hard, however still manage to land with sustained performances well above the peak performances of the competition.

GFXBench Aztec Ruins - High - Vulkan/Metal - Off-screen

In GFXBench Aztec High, the 13 Pro lands in at a massive +46% performance advantage over the 12 Pro, while the 13 showcases a +19% boost. These are numbers that are above the expectations – in terms of microarchitectural changes the new A15 GPU appears to adopt the same double FP32 throughput as on the M1 GPU, seemingly adding extra units alongside the existing FP32/double-rate FP16 ALUs. The increased 32MB SLC will also likely help a lot with GPU bandwidth and hit-rates, so these two changes seem to be the most obvious explanations for the massive increases.

In terms of power and efficiency, I’m also migrating away from tables to bubble charts to better represent the spatial positioning of the various SoCs.

I’d also like to note here that I had went ahead and re-measured the A13 and A14 phones in their peak performance states, showcasing larger power figures than the ones we’ve published in the past. Reason for this is the methodology where we’re only able to measure via input power of the phone, as we cannot dismantle our samples and are lacking PMIC fuelgauge access otherwise. The iPhone 13 figures here are generally hopefully correct as I measured other scenarios up to 9W, however there is still a bit of doubt on whether the phone is drawing from battery or not. The sustained power figures have a higher reliability.

As noted, the A15’s peak performance is massively better, but also appearing that the phone is improving the power draw slightly compared to the A14, meaning we see large efficiency improvements.

Both the 13 and 13 Pro throttle quite quickly after a few minutes of load, but generally at different power points. The 13 Pro with its 5-core GPU throttles down to around 3W, while the 13 goes to around 3.6W.

GFXBench Aztec Ruins - Normal - Vulkan/Metal - Off-screen

In Aztec Normal, we’re seeing similar relative positioning both in performance and efficiency. The iPhones 13 and 13 Pro are quite closer in performance than expected, due to different throttling levels.

GFXBench Manhattan 3.1 Off-screen

Finally, in Manhattan 3.1, the A15’s 5-core goes up +32%, while the 4-core goes up +18%. The sustained performance isn’t notably different between the two, and also represent smaller improvements over the iPhone 11 and 12 series.

Impressive GPU Performance, but quite limited thermals

Our results here showcase two sides of a coin: In terms of peak performance, the new A15 GPU is absolutely astonishing, and showcasing again improvements that are well above Apple’s marketing claims. The new GPU architecture, and possibly the new SLC allow for fantastic gains in performance, as well as efficiency.

What’s not so great, is the phone’s throttling. Particularly, we seem to be seeing quite reduced power levels on the iPhone 13 Pro, compared to the iPhone 13 as well as previous generation iPhones.

Source: 微机分WekiHome

The 13 Pro models this year come with a new PCB design, that’s even denser than what we’ve had on the previous generations, in order to facilitate the larger battery and new camera modules. What’s been extremely perplexing with Apple’s motherboard designs has been the fact that since they employed dual-layer “sandwich” PCBs, is that they’re packaging the SoC on the inside of the two soldered boards. This comes in contrast to other vendors such as Samsung, who also have adopted the “sandwich” PCB, but the SoC is located on the outer side of the assembly, making direct contact with the heat spreader and display mid-frame.

There are reports of the new iPhones throttling more under gaming and cellular connectivity – well, I’m sure that having the modem directly opposite the SoC inside the sandwich is a contributor to this situation. The iPhone 13 Pro showcasing lower sustained power levels may be tied to the new PCB design, and Apple’s overall iPhone thermal design is definitely amongst the worst out there, as it doesn’t do a good job of spreading the heat throughout the body of the phone, achieving a SoC thermal envelope that’s far smaller than the actual device thermal envelope.

No Apples to Apples in Gaming

In terms of general gaming performance, I’ll also want to make note of a few things – the new iPhones, even with their somewhat limited thermal capacity, are still vastly faster than give out a better gaming experience than competitive phones. Lately benchmarking actual games has been something that has risen in popularity, and generally, I’m all for that, however there are just some fundamental inconsistencies that make direct game comparisons not empirically viable to come to SoC conclusions.

Take Genshin Impact for example, unarguably the #1 AAA mobile game out there, and also one of the most performance demanding titles in the market right now, comparing the visual fidelity on a Galaxy S21 Ultra (Snapdragon 888), Mi 11 Ultra, and the iPhone 13 Pro Max:

Galaxy S21 Ultra - Snapdragon 888

Mi 11 Ultra - Snapdragon 888

Even though the S21 Ultra and the Mi 11 Ultra both feature the same SoC, they have very different characteristics in terms of thermals. The S21 Ultra generally sustains about 3.5W total device power under the same conditions, while the Mi 11 Ultra will hover between 5-6W, and a much hotter phone. The difference between the two not only exhibits itself in the performance of the game, but also in the visual fidelity, as the S21 Ultra is running much lower resolution due to the game having a dynamic resolution scaling (both phones had the exact same game settings).

iPhone 13 Pro Max - A15

The comparison between Android phones and iPhones gets even more complicated in that even with the same game setting, the iPhones still have slightly higher resolution, and visual effects that are just outright missing from the Android variant of the game. The visual fidelity of the game is just much higher on Apple’s devices due to the superior shading and features.

In general, this is one reason while I’m apprehensive of publishing real game benchmarks as it’s just a false comparison and can lead to misleading conclusions. We use specifically designed benchmarks to achieve a “ground truth” in terms of performance, especially in the context of SoCs, GPUs, and architectures.

The A15 continues to cement Apple’s dominance in mobile gaming. We’re looking forward to the next-gen competition, especially RDNA-powered Exynos phones next year, but so far it looks like Apple has an extremely comfortable lead to not have to worry much.

CPU ST Performance: Faster & More Efficient Conclusion & End Remarks
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  • Andrei Frumusanu - Monday, October 4, 2021 - link

    I didn't see much difference on the Max. The issue is chip to body dissipation, not total body to ambient dissipation.
  • cha0z_ - Monday, October 4, 2021 - link

    Yeah, guessed that much, but still had hopes. Basically the sustained GPU performance is just a tad higher vs my 11 pro max and I am kinda sad about it even with all the other improvements. :(

    There are super good, but GPU demanding games like x-com 2 WOTC, not to mention for the 120Hz scenario, but even if more efficient the FPS number when you play for more than 10m will be indistinguishable if no FPS counter is visible.

    Correct me if I am wrong and if not a big hassle given I really respect your opinion and work + you have experience with 11 pro max also - do you think it's a decent overall upgrade (simple yes/no will do. I am power user + got 2233rz 120Hz at launch :) ). Especially by feel how do you compare them in gaming?

    Also cheers for your great articles and deep dives! Love them all!
  • repoman27 - Monday, October 4, 2021 - link

    Not arguing one way or the other as to the merits of Apple's thermal solution, but the side of the A15 package which faces the interior of the PCB sandwich is a PoP with 4 SDRAM dies in it. The business side of the SoC is attached to a very thin PCB via InFO. The opposite side of the PCB in the region where the SoC is located has very little active circuitry other than the audio chips and secure element. However, it does have a can with thermal pads to help transfer the heat from the SoC upwards through the screen.

    In other words, I believe most of the heat from the SoC is radiated upwards through the screen / top of the device, while the heat from the modem / RF transceiver chips is radiated through the back glass / bottom of the device.
  • Andrei Frumusanu - Monday, October 4, 2021 - link

    We can theorize, but at the end of the day it's got far lower sustained power than any other phone and there are thermal issues that Apple has encountered several times now, some not addressed in articles.
  • repoman27 - Monday, October 4, 2021 - link

    I have no idea if Apple made good decisions regarding thermals in this case or not, and I'm glad you're investigating / reporting on the topic. However, by constantly pushing density further than everyone else and using technologies like InFO and substrate-like PCBs, Apple may be solving for a slightly different set of problems than their competitors.
  • teldar - Wednesday, October 6, 2021 - link

    It's not really Apple pushing density. It's the processor manufacturer. That's a little misleading.
  • Ppietra - Wednesday, October 6, 2021 - link

    teldar, it’s both! It is up to Apple to decide which node it wants to use.
  • Spunjji - Friday, October 8, 2021 - link

    @Ppietra & teldar - I think repoman27 meant "pushing density" in terms of PCB layout and design, rather than the node the CPU is manufactured on.
  • unclevagz - Monday, October 4, 2021 - link

    How does the Spec 2017 performance here compare against x86 (Zen 3/RKL)?
  • Andrei Frumusanu - Monday, October 4, 2021 - link

    Comparative subsets would 5950X 7.29 int / 9.79 fp, 11900K 6.61 int / 9.58 fp. versus 7.28 / 10.15 on A15.

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