A few weeks ago, we’ve seen Apple announce their newest iPhone 13 series devices, a set of phones being powered by the newest Apple A15 SoC. Today, in advance of the full device review which we’ll cover in the near future, we’re taking a closer look at the new generation chipset, looking at what exactly Apple has changed in the new silicon, and whether it lives up to the hype.

This year’s announcement of the A15 was a bit odder on Apple’s PR side of things, notably because the company generally avoided making any generational comparisons between the new design to Apple’s own A14. Particularly notable was the fact that Apple preferred to describe the SoC in context of the competition; while that’s not unusual on the Mac side of things, it was something that this year stood out more than usual for the iPhone announcement.

The few concrete factoids about the A15 were that Apple is using new designs for their CPUs, a faster Neural engine, a new 4- or 5-core GPU depending on the iPhone variant, and a whole new display pipeline and media hardware block for video encoding and decoding, alongside new ISP improvements for camera quality advancements.

On the CPU side of things, improvements were very vague in that Apple quoted to be 50% faster than the competition, and the GPU performance metrics were also made in such a manner, describing the 4-core GPU A15 being +30% faster than the competition, and the 5-core variant being +50% faster. We’ve put the SoC through its initial paces, and in today’s article we’ll be focusing on the exact performance and efficiency metrics of the new chip.

Frequency Boosts; 3.24GHz Performance & 2.0GHz Efficiency Cores

Starting off with the CPU side of things, the new A15 is said to feature two new CPU microarchitectures, both for the performance cores as well as the efficiency cores. The first few reports about the performance of the new cores were focused around the frequencies, which we can now confirm in our measurements:

Maximum Frequency vs Loaded Threads
Per-Core Maximum MHz
Apple A15 1 2 3 4
Performance 1 3240 3180    
Performance 2   3180    
         
Efficiency 1 2016 2016 2016 2016
Efficiency 2   2016 2016 2016
Efficiency 3     2016 2016
Efficiency 4       2016
Maximum Frequency vs Loaded Threads
Per-Core Maximum MHz
Apple A14 1 2 3 4
Performance 1 2998 2890    
Performance 2   2890    
         
Efficiency 1 1823 1823 1823 1823
Efficiency 2   1823 1823 1823
Efficiency 3     1823 1823
Efficiency 4       1823

Compared to the A14, the new A15 increases the peak single-core frequency of the two-performance core cluster by 8%, now reaching up to 3240MHz compared to the 2998MHz of the previous generation. When both performance cores are active, their operating frequency actually goes up by 10%, both now running at an aggressive 3180MHz compared to the previous generation’s 2890MHz.

In general, Apple’s frequency increases here are quite aggressive given the fact that it’s quite hard to push this performance aspect of a design, especially when we’re not expecting major performance gains on the part of the new process node. The A15 should be made on an N5P node variant from TSMC, although neither company really discloses the exact details of the design. TSMC claims a +5% frequency increase over N5, so for Apple to have gone further beyond this would have indicated an increase in power consumption, something to keep in mind of when we dive deeper into the power characteristics of the CPUs.

The E-cores of the A15 are now able to clock up to 2016MHz, a 10.5% increase over the A14’s cores. The frequency here is independent of the performance cores, as in the number of threads in the cluster doesn’t affect the other cluster, or vice-versa. Apple has done some more interesting changes to the little cores this generation, which we’ll come to in a bit.

Giant Caches: Performance CPU L2 to 12MB, SLC to Massive 32MB

One more straightforward technical detail Apple revealed during its launch was that the A15 now features double the system cache compared to the A14. Two years ago we had detailed the A13’s new SLC which had grown from 8MB in the A12 to 16MB, a size that was also kept constant in the A14 generation. Apple claiming they’ve doubled this would consequently mean it’s 32MB now in the A15.

Looking at our latency tests on the new A15, we can indeed now confirm that the SLC has now doubled up to 32MB, further pushing the memory depth to reach DRAM. Apple’s SLC is likely to be a key factor in the power efficiency of the chip, being able to keep memory accesses on the same silicon rather than going out to slower, and more power inefficient DRAM. We’ve seen these types of last-level caches being employed by more SoC vendors, but at 32MB, the new A15 dwarfs the competition’s implementations, such as the 3MB SLC on the Snapdragon 888 or the estimated 6-8MB SLC on the Exynos 2100.

What Apple didn’t divulge, is also changes to the L2 cache of the performance cores, which has now grown by 50% from 8MB to 12MB. This was actually the same L2 size as on the Apple M1, only this time around it’s serving only two performance cores rather than four. The access latency appears to have risen from 16 cycles on the A14 to 18 cycles on the A15. 

A 12MB L2 is again humongous, over double compared to the combined L3+L2 (4+1+3x0.5 = 6.5MB) of other designs such as the Snapdragon 888. It very much appears Apple has invested a lot of SRAM into this year’s SoC generation.

The efficiency cores this year don’t seem to have changed their cache sizes, remaining at 64KB L1D’s and 4MB shared L2’s, however we see Apple has increased the L2 TLB to 2048 entries, now covering up to 32MB, likely to facilitate better SLC access latencies. Interestingly, Apple this year now allows the efficiency cores to have faster DRAM access, with latencies now at around 130ns versus the +215ns on the A14, again something to keep in mind of in the next performance section of the article.

CPU Microarchitecture Changes: A Slow(er) Year?

This year’s CPU microarchitectures were a bit of a wildcard. Earlier this year, Arm had announced the new Armv9 ISA, predominantly defined by the new SVE2 SIMD instruction set, as well as the company’s new Cortex series CPU IP which employs the new architecture. Back in 2013, Apple was notorious for being the first on the market with an Armv8 CPU, the first 64-bit capable mobile design. Given that context, I had generally expected this year’s generation to introduce v9 as well, but however that doesn’t seem to be the case for the A15.

Microarchitecturally, the new performance cores on the A15 doesn’t seem to differ much from last year’s designs. I haven’t invested the time yet to look at every nook and cranny of the design, but at least the back-end of the processor is identical in throughput and latencies compared to the A14 performance cores.

The efficiency cores have had more changes, alongside some of the memory subsystem TLB changes, the new E-core now gains an extra integer ALU, bringing the total up to 4, up from the previous 3. The core for some time no longer could be called “little” by any means, and it seems to have grown even more this year, again, something we’ll showcase in the performance section.

The possible reason for Apple’s more moderate micro-architectural changes this year might be a storm of a few factors – Apple had notably lost their lead architect on the big performance cores, as well as parts of the design teams, to Nuvia back in 2019 (later acquired by Qualcomm earlier this year). The shift towards Armv9 might also imply some more work done on the design, and the pandemic situation might also have contributed to some non-ideal execution. We’ll have to examine next year’s A16 to really determine if Apple’s design cadence has slowed down, or whether this was merely just a slippage, or simply a lull before a much larger change in the next microarchitecture.

Of course, the tone here paints rather conservative improvement of the A15’s CPUs, which when looking at performance and efficiency, are anything but that.

CPU ST Performance: Faster & More Efficient
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  • jarumbo13 - Monday, October 4, 2021 - link

    A real Apple only has one core and more pips than are mentioned in these specs. Reply
  • melgross - Monday, October 4, 2021 - link

    Will you be able to test any of the other components in the chip? It seems to me that year after year, Apple is subordinating what were CPU functions to their other subsystems, such the neural engine, machine learning modules, ISP, etc.

    It could be why Apple seems to be looking at bigger advances in these areas when compared to the CPUs.
    Reply
  • chief-worminger - Monday, October 4, 2021 - link

    Excellent article, as objective and comprehensive as ever. Does anyone know what the general estimated % edge the N5P and/or N5 nodes have over Samsung's 5LPE (or any more recent) node? I'm trying to imagine an X1/X2 core might be able to achieve on the various nodes, just to try to imagine what the next couple of year's worth of potential is.

    What might a Cortex X2 on N5P score on Geekbench5, for example?

    Also anyone know when Samsung's 3GAE or TSMC's next (3nm?) node is going to be available on flagship SoCs?
    Reply
  • tipoo - Monday, October 4, 2021 - link

    I used to get excited by silicon improvements, I guess I still do to a lesser extent, but now it's like, all this buildup and what am I going to use it for? I still use the browser, Messages, some social media, and that's pretty well that.

    Nothing on Apple Arcade really drew me in more than your typical mobile fare. What I'd really like to see them do now is lean into the controller grip setup and fund some AAA tier exclusives for Apple Silicon, including Apple TV, iPads, iPhones, and Macbooks in that definition. Something that really stretches that silicon muscle, maybe A12+ required, the Switch is far weaker than any of these by now but that gets AAA titles still while iPhones usually don't.

    Be nice if Tim Apple splashed that dragons hoard of gold around on some bespoke exclusives that really used their modern A/M chips.
    Reply
  • michael2k - Monday, October 4, 2021 - link

    What do you suggest? From my perspective they’re selling you six years of OS updates, while the article already mentions GI. GI already has PS specific content so maybe that would work? Reply
  • tipoo - Monday, October 4, 2021 - link

    Apple funded exclusives that take fuller advantage of the hardware, which I already suggested Reply
  • michael2k - Monday, October 4, 2021 - link

    Right, but what game do you think will encourage people to buy more iPhones? That’s the kind of question I imagine Apple has to consider. I specifically mentioned Genshin Impact. Reply
  • Fulljack - Wednesday, October 6, 2021 - link

    why didn't I think of that? while A15 are currently the fastest smartphone chip, it won't be in the next 6 years, but at least it'll still perform well enough unlike the slug fest my 2 years old SD855 phone are. Reply
  • Alistair - Monday, October 4, 2021 - link

    100 percent agree with you. I love the silicon performance, but the problem is iOS. I love Fantasian, but I can't even back up my save files, or transfer them at will between devices. iOS sucks. That's the issue. One of the reasons people love Steam. How come 20 years later only Steam has a proper backup and restore function. Epic game store, Windows store, they've had decades, some are new, they still lack basic functionality. That's how I feel about iOS.

    iOS save files? Nope. iOS external 16:9 display support? Nope. 120hz external display support? Nope. Can I easily downgrade from the iOS beta? Nope. Does Apple sign your files and make them incompatible after using the beta? Yes. It's just a long list of annoyances, iOS.

    Get that CLOSED OS into a gaming device, and I'm not as irritated. The Switch is closed off also. Except you can actually export your save files on the Switch, but not with iOS. LOL.
    Reply
  • misan - Monday, October 4, 2021 - link

    That’s not really iOS problem though. The OS itself supports saving and exchanging files, but there is not much you can do if the developer of the game doesn’t support the file system. Reply

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