Apple's Swift: Visualized

Section by Anand Shimpi

Based on my findings on the previous pages, as well as some additional off-the-record data, this is what I believe Swift looks like at a high level:


Note that most of those blocks are just place holders as I don't know how they've changed from Cortex A9 to Swift, but the general design of the machine is likely what you see above. Swift moves from a 2-wide to a 3-wide machine at the front end. It remains a relatively small out-of-order core, but increases the number of execution ports from 3 in Cortex A9 to 5. Note the dedicated load/store port, which would help explain the tremendous gains in high bandwidth FP performance.

I asked Qualcomm for some additional details on Krait unfortunately they are being quite tight lipped about their architecture. Krait is somewhat similar to Swift in that it has a 3-wide front end, however it only has 4 ports to its 7 execution units. Qualcomm wouldn't give me specifics on what those 7 units were or how they were shared by those 4 ports. It's a shame that Intel will tell me just how big Haswell's integer and FP register files are 9 months before launch, but its competitors in the mobile SoC space are worried about sharing high level details of architectures that have been shipping for half a year.

Apple's Swift core is a wider machine than the Cortex A9, and seemingly on-par with Qualcomm's Krait. How does ARM's Cortex A15 compare? While the front end remans 3-wide, ARM claims a doubling of fetch bandwidth compared to Cortex A9. The A15 is also able to execute more types of instructions out of order, although admittedly we don't know Swift's capabilities in this regard. There's also a loop cache at the front end, something that both AMD and Intel have in their modern architectures (again, it's unclear whether or not Swift features something similar). ARM moves to three dedicated issue pools feeding 8 independent pipelines on the execution side. There are dedicated load and store pipelines, two integer ALU pipes, two FP/NEON pipes, one pipe for branches and one for all multiplies/divides. The Cortex A15 is simply a beast, and it should be more power hungry as a result. It remains to be seen how the first Cortex A15 based smartphone SoCs will compare to Swift/Krait in terms of power. ARM's big.LITTLE configuration was clearly designed to help mitigate the issues that the Cortex A15 architecture could pose from a power consumption standpoint. I suspect we haven't seen the end of NVIDIA's companion core either.

At a high level, it would appear that ARM's Cortex A15 is still a bigger machine than Swift. Swift instead feels like Apple's answer to Krait. The release cadence Apple is on right now almost guarantees that it will be a CPU generation behind in the first half of next year if everyone moves to Cortex A15 based designs.

Custom Code to Understand a Custom Core Apple's Swift: Pipeline Depth & Memory Latency
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  • dado023 - Tuesday, October 16, 2012 - link

    These days for me is battery life and then screen usability, so my next buy will be 720p, with iPhone5 setting the bar, i hope other android makers will follow. Reply
  • Krysto - Tuesday, October 16, 2012 - link

    Are you implying iPhone 5 is setting the bar for 720p displays? Because first of all, it doesn't have an 1280x720 resolution, but a 1136x640 one, and second, Android devices have been sporting 720p displays since a year ago. Reply
  • hapkiman - Tuesday, October 16, 2012 - link

    I have an iPhone 5 and my wife has a Samsung Galaxy S III.

    Her Galaxy S III has a Super AMOLED 1280x720 display.

    And yes my iPhone 5 "only" has a 1136 x 640 display.

    But guess what - I'm holding both phones side by side right now looking at the exact same game and there is no perceivable difference. I looked at it, my son looked at it, and my wife looked at it. On about five or six different games, videos, apps, and a few photos. The difference is academic. You cant tell a difference unless you have a bionic eye.

    They both look freakin' fantastic.
    Reply
  • reuthermonkey1 - Tuesday, October 16, 2012 - link

    I think you're missing Krysto's point. Of course looking at a 4" 1136 x 640 and a 4.8" 1280x720 display side by side will look equivalent to the eye. But his response wasn't to whether they're similar, but to the minimum requirement dado023 has set for their next purchase to be 720p.

    The iPhone5's screen looks fantastic, but it's not 720p, so it's not exactly setting the bar for 720p.
    Reply
  • Samus - Wednesday, October 17, 2012 - link

    I'm no Apple fan, but in their defense, it is completely unneccessary to have 720p resolution on a 4" screen.

    The ppi of the screen is already 20% higher than is discernible by the human eye. Having the resolution any higher would be a waste of processing power.
    Reply
  • afkrotch - Wednesday, October 17, 2012 - link

    More screen real estate. Higher resolution, more crap you can throw on it. Course ih a 4" or 4.8" display, how many icons can you really place on the screen. I have a 4" screen and I wished I could shrink my icons though. Would love to get more icons on there.

    I can't do large phones anymore. I had a 5" Dell Streak...no thanks. Too big.
    Reply
  • rarson - Wednesday, October 17, 2012 - link

    "The ppi of the screen is already 20% higher than is discernible by the human eye."

    Uh, no it's not. The resolution of a human retina is higher than 326 ppi.
    Reply
  • Silma - Thursday, October 18, 2012 - link

    This doesn't mean anything. It depends on how far away the reading material is from the eye.

    720p may not be needed for such a small screen but it is better than "not exactly" 720p in that the phone doesn't have to rescale 720p material.

    In the same way retina marketing for macbook is pure BS as for the screen size and eye distance from the screen such a high resolution is not needed and will only burn batteries faster and make laptops warmer for next to no visual benefit. In addition 1080p materials will have to be rescaled.
    Reply
  • rarson - Thursday, October 18, 2012 - link

    Right, so if you have good vision, like I do, then at a foot away, you can see those pixels. Reply
  • MobiusStrip - Friday, October 19, 2012 - link

    Yawn. Reply

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