iPhone to iPad: CPU Changes

Although the iPad Air uses the same A7 from the iPhone 5s (and M7 motion coprocessor), there are a few minor differences that do lead to better performance.

At a high level we’re still talking about two 64-bit Apple Cyclone cores with 128KB L1s (64KB I$ + 64KB D$) per core, a shared 1MB L2 cache and a 4MB L3 cache that services the entire SoC. Apple increased CPU frequency from 1.3GHz to 1.4GHz in the iPad Air, a mild increase but in line with what we’ve seen from previous iPad designs. That’s the first impact on performance - a 7.69% increase in CPU frequency.

The second impact on performance is something I only noticed while digging around under the hood of the A7. It seems like the implementation in the iPad Air can, for whatever reason, hold more instructions in flight (over 20% more) than the A7 in the iPhone 5s. It’s unclear to me whether the A7 in the iPad is configured any differently via firmware/microcode or if perhaps we’re looking at a slightly different revision of the core, but the delta was repeatable in my testing.

The third, and likely biggest change impacting the iPad Air’s implementation of the A7 is the additional thermal headroom afforded by the larger chassis. I’m not going to go into details on exactly what this next test does (unfortunately we’re going to occlude some of the low level work that we do in light of all of the benchmark cheating going on), but we’re looking at a curve of performance vs. time for a particularly power heavy mix of code. We’re running the same exact code on both the iPad Air and iPhone 5s here, the only real difference is the size of the chassis:

You can see the 5s throttles back its CPU frequency to about 1GHz after the 2 minute mark. The crazy thing is that until that point the 5s manages to run at full frequency without so much as a hiccup for two full minutes, running an incredibly power hungry task. Given that most iOS apps aren’t this power intensive for such a sustained period of time, iPhone 5s users should almost always see the A7 running at a full 1.3GHz. Pretty crazy.

The iPad Air by comparison shows much more controlled behavior. Early on in the test we see a 7.7% performance advantage, which lines up perfectly with the iPad Air’s 7.7% CPU frequency advantage. By the end of the test the iPhone 5s has throttled to 900MHz, while the iPad Air drops to around 1.2GHz. At this point the iPad Air’s performance advantage grows to almost 40%.

CPU Performance

I've gone through our standard set of cross-platform browser based benchmarks to place the iPad Air's performance in perspective. As I mentioned in our 5s review, I don't know that there are many (any?) applications on iOS 7 that can really take advantage of all the A7 has to offer. There's definitely a ton of headroom left in the design. What's particularly exciting is when the A7 ends up in n-1 or n-2 iOS devices and it becomes the minimum developer target going forward.

I won't go through all of the results here again, but it's safe to say that the iPad Air is the fastest ARM based tablet on the planet at this point.

SunSpider 1.0 Benchmark

SunSpider 0.9.1 Benchmark

Mozilla Kraken Benchmark (Stock Browser)

Google Octane v1

Browsermark 2.0

WebXPRT - Overall Score

 

A7 Power Consumption

I’ll get to battery life in a bit, but I’ve been curious about the dynamic range of power consumption offered by Apple’s new A7 SoC. On the one hand we’re dealing with a lower power process (28nm vs. 32nm), but on the other hand Apple’s Cyclone cores can clearly draw more power given how beefy the architecture is this round. Apple frowns upon review sample dissection so I had to turn to a less scientific method of external platform level power measurement. The fidelity of the numbers here aren’t all that great but it’s better than nothing.

For the first test I measured platform power consumption during a Kraken run:

I purposely started measuring before the benchmark so I could get an idea of idle power consumption. The iPad Air consumes roughly 72% of the idle power as the iPad 4, both running at the same brightness. Here we’re not just seeing the A7’s advantages but also things like lower display power.

Focusing on the load portion of the measurement we see that both the new iPad and old iPad consume the same total power in this test. I suspect the A7 is drawing more power than the A6X, but it’s masked by a lower power display. Given how much faster the iPad Air is, Apple’s latest tablet features far lower overall task energy than the outgoing iPad 4. This is probably both the best case scenario for the iPad Air and the most likely case as well.

For kicks I wanted to see just how much power I could get the iPad Air to draw. Here I’m looking at platform power during our mini-power-virus test from above:

How’s that for dynamic range? Almost 12W running all out, but around half that in what we’d normally consider to be a stressful CPU test. I couldn’t get any actual applications/games on the iPad Air to behave like this so the results above are purely academic (for now). A quick run through GFXBench 2.7’s T-Rex HD test confirms that even pushing the GPU won’t hit these numbers. The max I saw running T-Rex offscreen was ~6W, and turning to an actual game (Infinity Blade 3) the iPad Air pulls less than 5W.

 

An Update on Apple’s A7: It's Better Than I Thought GPU Performance
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  • eanazag - Monday, November 04, 2013 - link

    The innovation that the Thunderbolt people are really waiting for is faster eMMC flash on the iPad. USB 3 or Thunderbolt is not going to help the fact that the flash storage is too slow to even make USB 2 sweat. I completely agree that sync and restore via iTunes is painfully slow. I would also argue that WiFi sync on 2 stream N is useless if the iPad still sports slow storage.

    If I had a request for USB 3, it would solely based on higher power specs for charging or docking. I
    Reply
  • mnbob1 - Friday, November 08, 2013 - link

    Apple has put a lot of emphasis on iCloud and backing up to iCloud. I have an iPad and an IPhone and haven't connected either to my computer for over a year. I backup to iCloud and use iTunes Match to access my music library which also gives me ad free iTunes Radio now. I store photos to iCloud because I take advantage of Photo Stream. My documents are backed up to Drop Box. Earlier this year I upgraded from an iPhone 4S to and iPhone 5. With iCloud all of my device settings were restored within a few minutes and my apps were downloaded in the background so I could still use my phone while that was happening. With iTunes Match I was able to see my entire music library of over 7,000 songs and choose what I wanted to download to my phone when I wanted to. I was able to restore my photos quickly and access my documents from Dropbox quickly. The whole process took me less than an hour initially since I don't bog my phone down with a lot of apps that I don't use and I only download the music as I use it. I trying to figure out why you guys think you need to connect up with thunderbolt or USB 3.0 when the iPad Air also has wifi with MIMO capabilities. Stop tethering your portable devices to the desktop because Apple isn't going to do thunderbolt because it would exclude Windows PC's or upgrade to USB 3.0 because the need for data going across that wire becomes less important and it becomes more of a charging port. Reply
  • IUU - Sunday, November 17, 2013 - link

    I am glad you 're feeling so comfortable having your dafa stored on other people's hds.
    I suppose you feel comfortable, storing your food in other people's refrigerators,
    writing your diaries and personal notes on other people's diaries and notebooks.(Marx and Lenin would absolutely fall in love with you).
    And all this, despite the fact that your "entire music library" is laughably small to what an average local storage could offer. Oh I get it, you do this as a future proof policy, because you somehow know
    e storage won't improve in the future, despite the fact that the known laws of nature allow for much much more than zettabytes to be stored locally.
    Like the ignorant chinese peasant, thanking his lords for offering him 200 dollars instead of 100, you thank your cloud bosses for offering you 50 instead of 25gb. Sorry, but trying to convert the data network to a feudal type traditional energy grid won't work, because it's against the ways of nature.
    This energy grid is going to die soon as well, much to the dislike of the last remaining tyrants.
    Reply
  • pojkeboy - Wednesday, October 30, 2013 - link

    Ha. I love this comment. Reply
  • pdjblum - Wednesday, October 30, 2013 - link

    Despite the snap 600, the nexus 7.2 is still a wonderful device for a couple of hundred less than a mini with a reasonable amount of storage, not the pittance they offer in the base model. Not sure how he can recommend a mini at all when it is hundreds more than the nexus 7.2? The Verge will do that because they shit crApples, but a so called objective, highly intelligent reviewer should have a problem with that. Reply
  • akdj - Wednesday, October 30, 2013 - link

    The Nexus 7.2 is a POS. I returned mine within 3 weeks. 475,000 optimized tablet apps in the App Store, maybe 15 in the Play store. What a joke attempting to surf on the Nex7 in portrait. Decent performance, yeah....but without apps that aren't 'blown up' phone apps, it's a joke. With the mini, you're not just buying a quality built tablet (that is obviously more powerful than the Nex7), but into an extremely active and blossoming eco-system...now $50+ in 'free' productivity and creative apps optimized for the system...and phenomenal post purchase support. Google is selling their tabs right @ the cost of the BOM. Why? They're in it for YOUR personal info...they're miners, data miners. Your information is what they make their money on, not the hardware.
    While the Nex 7.2 maybe a decent choice for some looking to save a bit of cash, if you've got the money, the iPad is THEE only way to buy into the current tablet market. Period.
    Reply
  • pdjblum - Wednesday, October 30, 2013 - link

    crApple makes their money on ignorant, entitled, insecure people who want to pay extra to feel good about themselves. Reply
  • Scannall - Wednesday, October 30, 2013 - link

    Bitter much?

    Fact is, I don't mind paying more for a quality product with great service and support. With the added bonus of having apps I actually use, that have NO Android equivalents. Not to mention 16:9 form factor sucks for my tablet usage.

    I don't buy the cheapest car on the market either.
    Reply
  • jopamo - Sunday, November 03, 2013 - link

    "crApple doesn't make any money from me, yet I am equally ignorant, entitled, and insecure as the people I who claim want to pay extra to feel good about themselves."

    There. Fixed that for you. :)
    Reply
  • akdj - Monday, November 04, 2013 - link

    It's YOUR ignorance that shows---using 'crApple' and for YOU to decide folks' insecurities? I'm thinkin' you might be a bit secure---either that or you Mom said "HELL No!"....."If you want one, get a job, save some money---and buy it yourself!"
    Am I close? Certainly nailed YOUR insecurities...lol, always wonder about the ambiguity of the 'net and what these nay-sayers would actually have the Balls to say to an Apple owner in real life, face to face.
    pdjblum----Silly, Silly Boy
    Reply

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