A8’s CPU: What Comes After Cyclone?

Despite the importance of the CPU in Apple’s SoC designs, it continues to be surprising just how relatively little we know about their architectures even years after the fact. Even though the CPU was so important that Apple saw the need to create their own custom design, and then did two architectures in just the span of two years, they are not fond of talking about just what it is they have done with their architectures. This, unfortunately, is especially the case at the beginning of an SoC’s lifecycle, and for A8 it isn’t going to be any different.

Overall, from what we can tell the CPU in the A8 is not a significant departure from the CPU in A7, but that is not a bad thing. With Cyclone Apple hit on a very solid design: use a wide, high-IPC design with great latency in order to reach high performance levels at low clock speeds. By keeping the CPU wide and the clock speed low, Apple was able to hit their performance goals without having to push the envelope on power consumption, as lower clock speeds help keep CPU power use in check. It’s all very Intel Core-like, all things considered. Furthermore given the fact that Cyclone was a forward-looking design with ARMv8 AArch64 capabilities and already strong performance, Apple does not face the same pressure to overhaul their CPU architecture like other current ARMv7 CPU designers do.


Close Up: "Enhanced Cyclone"

As a result, from the information we have been able to dig up and the tests we have performed, the A8 CPU is not radically different from Cyclone. To be sure there are some differences that make it clear that this is not just a Cyclone running at slightly higher clock speeds, but we have not seen the same kind of immense overhaul that defined Swift and Cyclone.

Unfortunately Apple has tightened up on information leaks and unintentional publications more than ever with A8, so the amount of information coming out of Apple about this new core is very limited. In fact this time around we don’t even know the name of the CPU. For the time being we are calling it "Enhanced Cyclone" – it’s descriptive of the architecture – but we’re fairly certain that it does have a formal name within Apple to set it apart from Cyclone, a name we hope to discover sooner than later.

In any case one of the things we do know about Enhanced Cyclone is that unlike Apple’s GPU of choice for A8, Apple has seen a significant reduction in the die size of the CPU coming from the 28nm A7 to the 20nm A8. Chipworks’ estimates put the die size of Cyclone at 17.1mm2 versus 12.2mm2 for Enhanced Cyclone. On a relative basis this means that Enhanced Cyclone is 71% the size of Cyclone, which even after accounting for less-than-perfect area scaling still means that Enhanced Cyclone is a relatively bigger CPU composed of more transistors than Cyclone was. It is not dramatically bigger, but it’s bigger to such a degree that it’s clear that Apple has made further improvements over Cyclone.

The question of the moment is what Apple has put their additional transistors and die space to work on. Some of that is no doubt the memory interface, which as we’ve seen earlier L3 cache access times are nearly 20ns faster in our benchmarks. But if we dig deeper things start becoming very interesting.

Apple Custom CPU Core Comparison
  Apple A7 Apple A8
CPU Codename Cyclone "Enhanced Cyclone"
ARM ISA ARMv8-A (32/64-bit) ARMv8-A (32/64-bit)
Issue Width 6 micro-ops 6 micro-ops
Reorder Buffer Size 192 micro-ops 192 micro-ops?
Branch Mispredict Penalty 16 cycles (14 - 19) 16 (14 - 19)?
Integer ALUs 4 4
Load/Store Units 2 2
Addition (FP) Latency 5 cycles 4 cycles
Multiplication (INT) Latency 4 cycles 3 cycles
Branch Units 2 2
Indirect Branch Units 1 1
FP/NEON ALUs 3 3
L1 Cache 64KB I$ + 64KB D$ 64KB I$ + 64KB D$
L2 Cache 1MB 1MB
L3 Cache 4MB 4MB

First and foremost, in much of our testing Enhanced Cyclone performs very similarly to Cyclone. Accounting for the fact that A8 is clocked at 1.4GHz versus 1.3GHz for A7, in many low-level benchmarks the two perform as if they are the same processor. Based on this data it looks like the fundamentals of Cyclone have not been changed for Enhanced Cyclone. Enhanced Cyclone is still a very wide six micro-op architecture, and branch misprediction penalties are similar so that it’s likely we’re looking at the same pipeline length.

However from our low-level tests two specific features stand out: integer multiplication and floating point addition. When it comes to integer multiplication Cyclone had a single multiplication unit and it took four cycles to execute. However against Enhanced Cyclone those operations are now measuring in at three cycles to execute. But more surprising is the total Integer multiplication throughput rate; integer multiplication performance has now more than doubled. While this doesn’t give us enough data to completely draw out Enhanced Cyclone’s integer pathways, all of the data points to Enhanced Cyclone doubling up on its integer multiplication units, meaning Apple’s latest architecture now has two such units.

Meanwhile floating point addition shows similar benefits, though not as great as integer multiplication. Throughput is such that there appears to still be three FP ALUs, but like integer multiplication the instruction latency has been reduced. Apple has managed to shave off a cycle on FP addition, so it now completes in four cycles instead of five. Both of these improvements indicate that Enhanced Cyclone is not identical to Cyclone – the additional INT MUL unit in particular – making them very similar but still subtly different CPU architectures.


Apple iPhone Performance Estimates: Over The Years

Outside of these low-level operations, most other aspects of Enhanced Cyclone seem unchanged. L1 cache remains at 64KB I$ + 64KB D$ per CPU core, where it was most recently doubled for Cyclone. For L2 cache Chipworks believes that there may be separate L2 caches for each CPU core, and while L2 cache bandwidth is looking a little better on Enhanced Cyclone than on Cyclone, it’s not a “smoking gun” that would prove the presence of separate L2 caches. And of course, the L3 cache stands at 4MB, with the aforementioned improvements in latency that we’ve seen.

To borrow an Intel analogy once more, the layout and performance of Enhanced Cyclone relative to Cyclone is quite similar to Intel’s more recent ticks, where smaller feature improvements take place alongside a die shrink. In this case Apple has their die shrink to 20nm; meanwhile they have made some small tweaks to the architecture to improve performance across several scenarios. At the same time Apple has made a moderate bump in clock speed from 1.3GHz to 1.4GHz, but it’s nothing extreme. Ultimately while two CPU architectures does not constitute a pattern, if Apple were to implement tick-tock then this is roughly what it would look like.

Moving on, after completing our low-level tests we also wanted to spend some time comparing Enhanced Cyclone with its predecessor on some high level tests. The low-level tests can tell us if individual operations have been improved while high level tests can tell us something about what the performance impact will be in realistic workloads.

For our first high level benchmark we turn to SPECint2000. Developed by the Standard Performance Evaluation Corporation, SPECint2000 is the integer component of their larger SPEC CPU2000 benchmark. Designed around the turn of the century, officially SPEC CPU2000 has been retired for PC processors, but with mobile processors roughly a decade behind their PC counterparts in performance, SPEC CPU2000 is currently a very good fit for the capabilities of Cyclone and Enhanced Cyclone.

SPECint2000 is composed of 12 benchmarks which are then used to compute a final peak score. Though in our case we’re more interested in the individual results.

SPECint2000 - Estimated Scores
  A8 A7 % Advantage
164.gzip
842
757
11%
175.vpr
1228
1046
17%
176.gcc
1810
1466
23%
181.mcf
1420
915
55%
186.crafty
2021
1687
19%
197.parser
1129
947
19%
252.eon
1933
1641
17%
253.perlbmk
1666
1349
23%
254.gap
1821
1459
24%
255.vortex
1716
1431
19%
256.bzip2
1234
1034
19%
300.twolf
1633
1473
10%

Keeping in mind that A8 is clocked 100MHz (~7.7%) higher than A7, all of the SPECint2000 benchmarks show performance gains above and beyond the clock speed increase, indicating that every benchmark has benefited in some way. Of these benchmarks MCF, GCC, PerlBmk and GAP in particular show the greatest gains, at anywhere between 20% and 55%. Roughly speaking anything that is potentially branch-heavy sees some of the smallest gains while anything that plays into the multiplication changes benefits more.

MCF, a combinatorial optimization benchmark, ends up being the outlier here by far. Given that these are all integer benchmarks, it may very well be that MCF benefits from the integer multiplication improvements the most, as its performance comes very close to tracking the 2X increase in multiplication throughput. This also bodes well for any other kind of work that is similarly bounded by integer multiplication performance, though such workloads are not particularly common in the real world of smartphone use.

Our other set of comparison benchmarks comes from Geekbench 3. Unlike SPECint2000, Geekbench 3 is a mix of integer and floating point workloads, so it will give us a second set of eyes on the integer results along with a take on floating point improvements.

Geekbench 3 - Integer Performance
  A8 A7 % Advantage
AES ST
992.2 MB/s
846.8 MB/s
17%
AES MT
1.93 GB/s
1.64 GB/s
17%
Twofish ST
58.8 MB/s
55.6 MB/s
5%
Twofish MT
116.8 MB/s
110.0 MB/s
6%
SHA1 ST
495.1 MB/s
474.8 MB/s
4%
SHA1 MT
975.8 MB/s
937 MB/s
4%
SHA2 ST
109.9 MB/s
102.2 MB/s
7%
SHA2 MT
219.4 MB/
204.4 MB/s
7%
BZip2Comp ST
5.24 MB/s
4.53 MB/s
15%
BZip2Comp MT
10.3 MB/s
8.82 MB/s
16%
Bzip2Decomp ST
8.4 MB/
7.6 MB/s
10%
Bzip2Decomp MT
16.5 MB/s
15 MB/s
10%
JPG Comp ST
19 MP/s
16.8 MPs
13%
JPG Comp MT
37.6 MP/s
33.3 MP/s
12%
JPG Decomp ST
45.9 MP/s
39 MP/s
17%
JPG Decomp MT
89.3 MP/s
77.1 MP/s
15%
PNG Comp ST
1.26 MP/s
1.14 MP/s
10%
PNG Comp MT
2.51 MP/s
2.26 MP/s
11%
PNG Decomp ST
17.4 MP/s
15.1 MP/s
15%
PNG Decomp MT
34.3 MPs
29.6 MP/s
15%
Sobel ST
71.7 MP/s
58.1 MP/s
23%
Sobel MT
137.1 MP/s
112.4 MP/s
21%
Lua ST
1.64 MB/s
1.34 MB/s
22%
Lua MT
3.22 MB/s
2.64 MB/s
21%
Dijkstra ST
5.57 Mpairs/s
4.04 Mpairs/s
37%
Dijkstra MT
9.43 Mpairs/s
7.26 Mpairs/s
29%

Geekbench’s integer results are overall a bit more muted than SPECint2000’s, but there are still some definite high points and low points among these benchmarks. Crypto performance is among the lesser gains, while Sobel and Dijkstra are among the largest at 21% and 37% respectively. Interestingly in the case of Dijkstra, this does make up for the earlier performance loss Cyclone saw on this benchmark in the move to 64-bit.

Geekbench 3 - Floating Point Performance
  A8 A7 % Advantage
BlackScholes ST
7.85 Mnodes/s
5.89 Mnodes/s
33%
BlackScholes MT
15.5 Mnodes/s
11.8 Mnodes/s
31%
Mandelbrot ST
1.18 GFLOPS
929.4 MFLOPS
26%
Mandelbrot MT
2.34 GFLOPS
1.85 GFLOPS
26%
Sharpen Filter ST
981.7 MFLOPS
854 MFLOPS
14%
Sharpen Filter MT
1.94 MFLOPS
1.7 GFLOPS
14%
Blur Filter ST
1.41 GFLOPS
1.26 GFLOPS
11%
Blur Filter MT
2.78 GFLOPS
2.49 GFLOPS
11%
SGEMM ST
3.83 GFLOPS
3.44 GFLOPS
11%
SGEMM MT
7.48 GFLOPS
6.4 GFLOPS
16%
DGEMM ST
1.87 GFLOPS
1.68 GFLOPS
11%
DGEMM MT
3.61 GFLOPS
3.14 GFLOPS
14%
SFFT ST
1.77 GFLOPS
1.59 GFLOPS
11%
SFFT MT
3.47 GFLOPS
3.18 GFLOPS
9%
DFFT ST
1.68 GFLOPS
1.47 GFLOPS
14%
DFFT MT
3.29 GFLOPS
2.93 GFLOPS
12%
N-Body ST
735.8 Kpairs/s
587.8 Kpairs/s
25%
N-Body MT
1.46 Mpairs/s
1.17 Mpairs/s
24%
Ray Trace ST
2.76 MP/s
2.23 MP/s
23%
Ray Trace MT
5.45 MP/s
4.49 MP/s
21%

While the low-level floating point tests we ran earlier didn’t show as significant a change in the floating point performance of the architecture as it did the integer, our high level benchmarks show that floating point tests are actually faring rather well. Which goes to show that not everything can be captured in low level testing, especially less tangible aspects such as instruction windows. More importantly though this shows that Enhanced Cyclone’s performance gains aren’t just limited to integer workloads but cover floating point as well.

Overall, even without a radical change in architecture, thanks to a combination of clock speed increases, architectural optimizations, and memory latency improvements, Enhanced Cyclone as present in the A8 SoC is looking like a solid step up in performance from Cyclone and the A7. Over the next year Apple is going to face the first real competition in the ARMv8 64-bit space from Cortex-A57 and other high performance designs, and while it’s far too early to guess how those will compare, at the very least we can say that Apple will be going in with a strong hand. More excitingly, most of these performance improvements build upon Apple’s already strong single-threaded IPC, which means that in those stubborn workloads that don’t benefit from multi-core scaling Apple is looking very good.

A8: Apple’s First 20nm SoC A8’s GPU: Imagination Technologies’ PowerVR GX6450
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  • bobobobo - Tuesday, September 30, 2014 - link

    solid phone, solid improvement. Reply
  • AppleCrappleHater2 - Tuesday, September 30, 2014 - link

    Worship the holy apple.

    The apple way, selling over expensive crap to stupid consumers that like to
    get robbed.

    This has been a disastrous launch in every respect. The iwatch is such an
    ugly piece of crap, it is truly unbelievable how a company, formerly known for
    its remarkable design, dares to put out such a crap ton of shit. Some
    characteristics are glaringly obvious and inherent to it: over expensive,
    hardly innovative, limited functionality and usability (need of an iPhone to
    make it work), looks exactly like a toy watch and so on.

    There are of course way better smart watches out there, especially from the
    likes of Samsung, Sony, Motorola, Asus, LG, simply put, there is no need for
    another piece of over expensive junk.

    The iPhone 6 is technologically stuck in pre-2011 times, a base model with
    a capacity of 16GB without the possibility to use SD cards isn't even funny
    anymore. The screen resolution is horrendous, it isn't water proof, shock and
    dust resistant, it offers nothing innovative, just some incremental
    updates over its predecessor, both lacking severely behind their competitors at
    their respective launch dates.

    Now the Iphone 6 Plus offers a „Retina HD“ screen, full 1920x1080p, oh wow,
    where have you been for the past 4 years apple, talk about trailing behind.
    That’s pathetic. The interesting thing about that is the fact that apple
    always manages to sell backwards oriented, outdated crap to its user base, all
    while pretending to be an innovative technology leader. The similarities
    regarding any form of sectarian cult are striking.

    You gotta love how Apple always comes up with new marketing bullshit terms,
    aka "Retina HD", with the intention to manipulate its users while preventing easy
    comparisons with its competitors by withholding the actual specs. Apparently it’s
    not enough to have a 1080p screen, you have to call it "Retina HD" to make those
    suckers buy it, otherwise someone could look at the 4K Amoled and Oled screens
    form LG and Samsung devices and get outright disappointed. Same goes for
    everything else. Every outdated „feature“ needs to get its own marketing label
    to persuade buyers with crappy „experience“ and „usability“ ads, while covering
    the truth with marketing gibberish, knowing full well that only a fraction of
    aforementioned buyers cares to look at the facts and dares to compare them.

    Car engines come to mind. For comparisons shake let’s look at a 1.0 liter, turbo
    charged petrol engine and a V8 compressor. What’s better should be obvious, but
    by calling the former an „ecobooster“, thus giving it a special marketing label,
    this joke becomes a „feature“, something positive that can be added tot the list
    of features of a car.

    By doing so a negative aspect is transformed into a positive one, the
    reality is distorted, non tech savvy buyers are manipulated and comparisons are
    made more difficult (another layer of marketing bullshit to overcome), well done
    marketing department. You see , if something is seriously lacking (of course for
    profit, what else), don’t bother explaining, just give it a nice marketing term, distort
    reality, make it a feature and call it a day. Fuck that!!

    FACT: Apple has been forced to copy Android in style and size for
    years because people abandoned their tired, moribund and fossilized
    devices for superior and innovative Android devices.

    Steve Jobs said no one should want a 7" tablet until everyone went and bought
    Android devices forcing Apple to copycat with the iPad Mini. Apple
    didn't think anyone wanted a phone screen larger than a business card
    until they all bought Androids thus forcing the arrival this week of the
    iPhone Galaxy and iPhone Galaxy Note clone phones.

    Swipe down notifications that don't interfere? Copied from Android and WebOS. Siri?
    Bought and ruined from a private developer; Google Now crushes it.
    3rd-party keyboards? Welcome to 2010, iChumps! Widgets? Welcome to 2009
    except you can't place them on your home screen. Live wallpapers and
    hidden icons? Maybe Apple will get around to copying those in iOS X in
    2016. Who knows.

    Apple lacks creativity and honest people acknowledge it. Steve Jobs gets credited as an
    innovator when all he was, was a huckster who'd spot someone else's tech, polish it up nicely,
    then slap a gnawed fruit logo on the back, charge a premium price and
    wait for the rubes like Jim Smith to hand over their cash like the good
    iSheep they are.

    But after that initial iteration, Apple is incapable of actually innovating something new.
    They literally cannot make a product until someone else shows them how and they copy it.
    They are also unable refine things because they believe to improve is to
    admit something was imperfect the first time. (This is why QuickTime 4
    had a legendarily terrible UI that was never changed through QT7 a
    decade later.) All they can do is make things incrementally thinner or
    faster but it's just minor refinements since they can't invest their way
    out of a wet paper bag.

    For all their squealing about Retina displays, they never even had a HD display until now;
    8th time is the charm, though you need the iPhone Galaxy Note to get the 1080p that many Android
    users have had for at least a year and is now considered
    bare-minimum spec. At the rate Apple drags along, QHD screens should
    arrive in 2018. Maybe. A graphic went around after the reveal comparing
    the iPhone Galaxy to the Nexus 4 from 2012. Exactly.

    The Apple Iphone 1 and Ipad 1 might have been innovative at their time,
    but since then, the bitten apple has been continuously rotting from the inside
    outwards, always swarmed by millions of Iworms which regale themselves with its
    rotten flesh, not forgetting all other Americans who support apple by means of
    their tax dollars to finance its bought US Treasury/Government bond interest rates.

    Last but not least, every Apple product includes a direct hotlink to the NSA,
    free of charge, something that might make it a good value, after all.

    Ceterum censeo Applem esse delendam.
    Reply
  • esterhasz - Tuesday, September 30, 2014 - link

    Since we're quoting Cato today, here's a good one: "grasp the subject, the words will follow". Reply
  • uhuznaa - Tuesday, September 30, 2014 - link

    You seem to be a tiny bit obsessed. Reply
  • iphone6splus - Tuesday, September 30, 2014 - link

    Yet, he didn't comment on Touch ID. Reply
  • kevin_newell - Thursday, October 09, 2014 - link

    Apple is lagging far behind it's competitors both in user satisfaction (source: http://www.consumertop.com/best-phone-guide/) and innovation. I mean, who was first with large screens and phone cameras that work well in low light? It sure wasn't Apple. Reply
  • Caliko - Tuesday, October 06, 2015 - link

    A large iPhone is NOT innovation.

    Sorry iPhoney fan.
    Reply
  • lowtolerance - Tuesday, September 30, 2014 - link

    I can recommend some good therapists. You need one. Reply
  • vickyksoni - Monday, March 20, 2017 - link

    you can also read more details about iphone 6 at https://smarttopten.com/ as they have lot more information Reply
  • melgross - Tuesday, September 30, 2014 - link

    You sir, are a complete idiot! Reply

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