Increased Dynamic Range: Understanding the Power Profile of Modern SoCs

Section by Anand Shimpi

The iPhone 4S greatly complicated the matter of smartphone power consumption. With the A5 SoC Apple introduced a much wider dynamic range of power consumption to the iPhone than we were previously used to. Depending on the workload, the A5 SoC could either use much more power than its predecessor or enjoy decreased overall energy usage. I began our battery life analysis last time with some graphs showing the power savings realized by a more power hungry, faster CPU.

The iPhone 5 doesn't simplify things any more. I believe the days of us having straightforward discussions about better/worse battery life are long gone. We are now firmly in the era of expanded dynamic range when it comes to smartphone power consumption. What do I mean by that? The best way to explain is to look at some data. The graphs below show total device power consumption over time for a handful of devices running the Mozilla Kraken javascript benchmark. Kraken is multithreaded and hits the CPU cores fairly well. The power profile of the benchmark ends up being very similar to loading a very js-heavy web page, although for a longer period of time. All of the device displays were calibrated to 200 nits, although obviously larger displays can consume more power.

Let's start out by just looking at the three most recent iPhone generations:

The timescale for this chart is just how long the iPhone 4 takes to complete the Kraken benchmark. The iPhone 4/4S performance gap feels a lot bigger now going back to the 4 than it did when the 4S launched, but that's how it usually seems to work. Note how tight the swings are between min and max power consumption on the iPhone 4 during the test. As a standalone device you might view the iPhone 4 as being fairly variable when it comes to power consumption but compared to the 4S and 5 it might as well be a straight line.

The 4S complicated things by consuming tangibly more power under load than the 4, but being fast enough to complete tasks in appreciably less time. In the case of this Kraken run, the 4S consumes more power than the 4, however it's able to go to sleep quicker than the 4 and thus draw less power. If we extended the timeline for the iPhone 4 significantly beyond the end of its benchmark run we'd see the 4S eventually come out ahead in battery life as it was able to race to sleep quicker. The reality is that with more performance comes increased device usage - in other words, it's highly unlikely that with a 50% gain in performance users are simply going to continue to use their smartphone the same way as they would a slower device. Usage (and thus workload) doesn't remain constant, it's somewhat related to response time.

The iPhone 5 brings new meaning to device level power consumption. With a larger display and much more powerful CPU, it can easily draw 33% more power than the 4S under load, on average. Note the big swings in power consumption during the test. The A6 SoC appears to be more aggressive in transitioning down to idle states than any previous Apple SoC, which makes sense given how much higher its peak power consumption can be. Looking at total energy consumed however, the iPhone 5 clearly has the ability to be more power efficient on battery. The 5 drops down to iPhone 4 levels of idle power consumption in roughly half the time of the iPhone 4S. Given the same workload that doesn't run indefinitely (or nearly indefinitely), the iPhone 5 will outlast the iPhone 4S on a single charge. Keep the device pegged however and it will die quicker.

Out of curiosity I wanted to toss in a couple of other devices based on NVIDIA and Qualcomm silicon to see how things change. I grabbed both versions of the HTC One X:

The Tegra 3 based One X actually performs very well in this test, but its peak power consumption is significantly worse than everything else. It makes sense given the many ARM Cortex A9 cores built on a 40nm G process running at high clock speeds on the Tegra 3.

The 28nm Snapdragon S4 (dual-core Krait) based One X gives us some very interesting results. Peak power consumption looks identical to the iPhone 5, however Apple is able to go into deeper sleep states than HTC can with its S4 platform. Performance is a little worse here but that could be a combination of SoC and software/browser. I used Chrome for all of the tests so it should be putting Android's best foot forward, but the latest update to Safari in iOS 6 really did boost javascript performance to almost untouchable levels.

At the end of the day, the power profile of the iPhone 5 appears to be very close to that of a modern Snapdragon S4 based Android smartphone. Any battery life gains that Apple sees are strictly as a result of software optimizations that lead to better performance or the ability to push aggressively to lower idle power states (or both). It shouldn't be very surprising that these sound like a lot of the same advantages Apple has when talking about Mac battery life as well. Don't let the CPU cores go to sleep and Apple behaves similarly to other device vendors, but it's really in idle time or periods of lighter usage that Apple is able to make up a lot of ground.

There's one member of the modern mobile SoC market that we haven't looked at thus far: Intel's Medfield. The data below isn't directly comparable to the data above, my measurement methods were a little different but the idea is similar - we're looking at device level power consumption over time while Kraken runs. Here I'm only focusing on the latest and greatest, the Atom based Motorola RAZR i, the Snapdragon S4 based Droid RAZR M and the iPhone 5. The RAZR i/M are nearly identical devices making this the perfect power profile comparison of Atom vs. Snapdragon S4. The RAZR i is also the first Atom Z2460 based part to turbo up to 2.0GHz.

Very interesting. Atom is the only CPU that can complete the Kraken benchmark in less time than Apple's Swift. Peak power consumption is definitely higher than both the Qualcomm and Apple devices, although Intel's philosophy is likely that the added power usage is worth it given the quicker transition to idle. Note that Atom is able to drive to a slightly lower idle level than the Snapdragon S4, although the Swift based iPhone 5 can still go lower.

At least based on this data, it looks like Intel is the closest to offering a real competitor to Apple's own platform from a power efficiency standpoint. We're a couple quarters away from seeing the next generation of mobile SoCs so anything can happen next round, but I can't stress enough that the x86 power myth has been busted at this point.

I will add that despite Intel's performance advantage here, I'm not sure it justifies the additional peak power consumption. The RAZR i ends up being faster than the iPhone 5 but it draws substantially more power in doing so, and the time savings may not necessarily offset that. We'll see what happens when we get to our battery life tests.

 

GPU Analysis/Performance Battery Life
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  • Calista - Sunday, October 21, 2012 - link

    English is not my native language (as I'm sure you have noticed) and so the flow in the language is far from flawless. But I still believe my opinions are valid and that the review was too long-winded.
  • Teknobug - Wednesday, October 17, 2012 - link

    I live in a big city and I don't know a single person that went and got the iPhone 5, most are happy with the iPhone 4 or whatever phone they're using, I don't see what's so great about the iPhone 5 other than it being built better than the iPhone 4's double sided glass structure (I've seen people drop their's on the train or sidewalk and it shattering on both sides!).

    And what now? iPad mini? I thought Apple wasn't interested in the 6-7" tablet market, Steve Jobs said 9" is small enough. I know Apple tried a 6" tablet a decade ago but the market wasn't read for it back then.
  • name99 - Wednesday, October 17, 2012 - link

    You know what AnandTech REALLY needs now?
    A comment moderation system like Ars Technica, so that low-content comments and commenters (like the above) can be suppressed.

    Teknobug is a PERFECT example of Ars' Troll Type #1: "Son of the "I don't even own a TV" guy: "

    This is the poster who thinks other people will find it interesting that he cares nothing about their discussion or their interests, and in fact judges himself as somehow morally superior as a result. The morphology of this on Ars Technica includes people popping into threads about Windows 8 to proclaim how they will never use Windows, people popping into threads about iOS 6 to proclaim that they never have and never will buy an Apple product, and people popping into Android related threads and claiming that they will never purchase "crappy plastic phones." In these cases, the posters have failed to understand that no one really cares what their personal disposition is on something, if they have nothing to add to the discussion.
  • ratte - Wednesday, October 17, 2012 - link

    yeah, my thoughts exactly.
  • worldbfree4me - Wednesday, October 17, 2012 - link

    I finished reading the review a few moments ago. Kudos again for a very thorough review, however I do a have a few questions and points that I would like to ask and make.

    Am I wrong to say, Great Job on Apple finally catching up to the Android Pack in terms of overall performance? The GS3, HTC X debuted about 6 months ago yes?

    Have these benchmark scores from the competing phones been updated to reflect the latest OS updates from GOOG such as OS 4.1.X aka Jelly Bean?

    Clearly the LG Optimus G is a preview of the Nexus 4,complete with a modern GPU In Adreno 320 and 2GB ram. I think based on history, the Nexus 4 will again serve as a foundation for all future Androids to follow. But again, good Job on Apple finally catching up to Android with the caveat being, iOS only has to push its performance to a 4inch screen akin to a 1080p LCD monitor verses a true gamers 1440p LCD Home PC setup. Ciao
  • Zinthar - Thursday, October 18, 2012 - link

    Caught up and passed, actually (if you were actually reading the review). As far as graphics are concerned, no smartphone has yet to eclipse the 4S's 543MP2 other than, of course, the iPhone 5.

    I have no idea what you're going on about with the Adreno 320, because that only gets graphics performance up to about the level of the PowerVR SGX 543MP2. Please see Anand's preview: http://www.anandtech.com/show/6112/qualcomms-quadc...
  • yottabit - Wednesday, October 17, 2012 - link

    Anand, as a Mech-E, I think somewhere the anodization facts in this article got very wonky

    I didn't have time to read thoroughly but I saw something about the anodized layer equaling half the material thickness? The idea of having half a millimeter anodized is way off the mark

    Typically there are two types of anodizing I use: regular, and "hard coat anodize" which is much more expensive

    If the iPhone is scuffing then it's definitely using regular anodizing, and the thickness of that layer is likely much less than .001" or one thousandth of an inch. More on the order of a ten-thousandth of an inch, actually. The thickness of traditional anodizing is so negligible that in fact most engineers don't even need to compensate for it when designing parts.

    Hard-coat anodize is a much more expensive process and can only result in a few darker colors, whereas normal anodizing has a pretty wide spectrum. Hard-coat thicknesses can be substantial, in the range of .001" to .003". This usually must be compensated for in the design process. Hard coat anodize results in a much flatter looking finish than typical anodize, and is also pretty much immune to scratches of any sort.

    Aluminum oxide is actually a ceramic which is harder than steel. So having a sufficient thickness of anodize can pretty much guarantee it won't be scratched under normal operating conditions. However it's much cheaper and allows more colors to do a "regular" anodize

    When I heard about scuffgate I immediately thought one solution would be to have a hardcoat anodize, but it would probably be cost prohibitive, and would alter the appearance significantly
  • guy007 - Wednesday, October 17, 2012 - link

    A little late to the party with the review, the iPhone 6 is almost out now...
  • jameskatt - Wednesday, October 17, 2012 - link

    Anand is pessimistic about Apple's ability to keep creating its own CPUs every year. But realize that the top two smartphone manufacturers (Apple and Samsung) are CRUSHING the competition. And BOTH create their own CPUs.

    Apple has ALWAYS created custom chips for its computers - except for a few years when Steve Jobs accidentally let their chip engineers go when they switched to Intel and Intel's motherboard designs.

    Apple SAVES a lot of money by designing its own chips because it doesn't have to pay the 3rd party profit on each chip.

    Apple PREVENTS Samsung from spying on its chip designs and giving the data to its own chip division to add to its own designs. This is a HUGE win given Samsung's copycat mentality.

    Apple can now always be a step ahead of the competition by designing its own chips. Realize that others will create copies of the ARM A15. But only Apple can greatly improve on the design. Apple, for example, greatly improved the memory subsystem on its own ARM chips. This is a huge weakness on otherARM chips. Apple can now custom design the power control as well - prolonging battery life even more. Etc. etc.
  • phillyry - Sunday, October 21, 2012 - link

    Good points re: copycat and profit margin savings.

    I've always been baffled by the fact that Apple outsources their part manufacturing to the competition. I know that Samsung is a huge OEM player but they are stealing Apple's ideas. They are doing a very good job of it and now improving on those ideas and techs, which is good for the consumer but still seems completely illogical to me from Apple's perspective. Must be the 20/20 hindsight kicking in again.

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