Monday, April 09, 2012

7 myths about quad-core phones (Smartphones Unlocked)

When HTC first announced that U.S. versions of the HTC One X wouldn't bear Nvidia's quad-core Tegra 3 processor, my gut reaction was: that's a darn shame.

I was looking at things the wrong way. If you're HTC or Nvidia, losing the bragging rights of introducing the U.S. to its first quad-core phone months before anyone else is a bummer. (Of course, with no quad-core phone in our market, it's still anyone's game.) But if you're the typical consumer, you might wonder how you pulled the short end of the stick. After all, the more processing cores, the better the phone, right?
If you're going to use the number of cores on your phone as the single metric for performance, you're doing it wrong. -- Greg Sullivan, Senior Product Manager for Microsoft
Maybe not. A tremendous amount of detailed architecture and circuitry go into processor chips, which can make understanding their exact effects on performance a serious undertaking for most. (Note, if you are, in fact, the type of consumer who could teach a class on processors, this article probably isn't for you.)

In the end, your smartphone's internal performance boils down to more than the number of cores. In the end, how well your phone performs depends on a delicate balance involving everything from your base chip and batteries to your operating system and even the people who code your favorite apps.

The first thing you need to know is that the presence of quad-core application processors will soon become a huge selling point for the most premium smartphones. We saw it happen a year ago with dual-core phones, and it's happening now. Once again, there are common myths surrounding the concept of quad-core. Before we bite into those, let's recap what makes quad-core such a big deal in today's smartphone story.

The theory of multicore processors is this: if you can divvy up multiple tasks, or even multiple steps that are part of the same task, you can finish the task faster.

Roughly imagine it as an assembly line production: instead of having one person do everything on their own (single core), you can have each member of a team do their part and finish faster as a whole (multicore).

Quad-core chips promise dramatically faster performance and better battery life. That's because as each core works less hard to accomplish a task, it draws less battery power than if fewer cores strained with heavier workloads apiece. The higher the battery draw per core, the faster you drain your battery.

In the real world, that means your phone should get faster thanks to the assembly line analogy, while depleting the battery slower. In addition, screen resolution should look sharper, photos and apps will load faster, you can stream HD videos smoother, and you'll be able to play games like a demon. Sounds good, right? Right. But the performance you get out of a chip isn't as simple as just piling on the cores.

Myth No. 1: A chip is a chip is a chip
At the heart of every mobile application processor is the even more elemental ARM processor that forms the building block for the final product we know as the quad-core chip (really, an entire system on a chip, often called an SoC.) ARM is the company that masterminds the layout design of the chips inside Android phones, Windows phones, and even Apple's iPhone 4S. Chipmakers license the set of instructions (and even the right to tweak these blueprint instructions), to integrate into their own final chip design.

Differentiation comes two ways. ARM designs different chip models with different architectures -- like the A8, A9, and A15 chips -- each more capable than its predecessor. As a starting point, says Samsung's Nick DiCarlo, you have to compare the architecture of each chip when comparing SoCs. A single-core A9 chip (also called Cortex-A9) will dominate a single-core A8 chip, and so on.

Modifications are a second way that chipmakers differentiate and fine tune their product's performance. Nvidia's claim to fame is a lower-powered fifth core on its Tegra 3 quad-core processor, which handles low-power tasks like background app updates.

Getting a license to deviate from ARM's raw instructions and managing everything from design of the entire ARM-based system to the final production is the path to even better performance, says Qualcomm's Raj Talluri, vice president of product management.

"We're able to get more performance with two processors than our competition can get with four," he said of Qualcomm. Although Talluri didn't say it outright, he could have easily been defending HTC's decision to use Qualcomm's Snapdragon S4 dual-core processor on the One X in the U.S. and Nvidia's quad-core Tegra 3 processor elsewhere. For their part, Nvidia recently bought licensing rights for ARM's faster A15 chip and Tegra 4 rumors are already coming to light.
The reality is that the quad-core could be better, it could be equal, or it could be appreciably worse. -- Nick DiCarlo, SamsungThe two paths to differentiating ARM-based chips make predicting performance slippery for the average phone buyer. According to the logic of chip math, a smartphone with a dual-core A15 processor should perform in line with a quad-core chip using an ARM A9 processor.
Specifically, the global version of HTC's One X uses Nvidia's quad-core Tegra 3 chip, which is based on ARM's Cortex-A9 processor. In the U.S., Qualcomm's dual-core Snapdragon S4 processor stems from an ARM Cortex-A15 chip. CNET hasn't had a chance to compare the two side by side, but Samsung's DiCarlo believes that the performance difference between the two chips will be imperceptible in real-world tests.

Myth No. 2: Doubling the chip doubles the performance

You double the number of chips when you evolve from single-core to dual-core and from dual-core to quad-core, but what you're not doubling are the rest of the resources. All cores still must share a single battery, one pool of memory, and so on.

If the entire system is efficient (more on that later), Qualcomm's Talluri told me, you will see increased performance. Just don't expect said performance to actually double.

Myth No. 3: All cores, all the time

The assembly line analogy to explain how four cores speed up processes on your smartphone is handy but incomplete. That's because no matter how many cores you have, there's only so much they can share tasks without the help of software.

First, the operating system itself has to support "multithreading"; that is, assigning each processing core a chunk of a task. The device manufacturer also gets into the game, adding some software layers to help the hardware and operating system communicate.

I spoke to five experts in the course of preparing this article, and they all emphasized the need for the developers who actually program the apps and games to code with multithreaded execution in mind.

The problem, says Greg Sullivan, senior product manager for Microsoft, is that writing code to take advantage of multiple processor cores makes writing apps much harder. Likewise, there's a lot more complexity in debugging apps when something goes wrong, a challenge that many app developers are reluctant to face.
Multicore won't help you in a world where the apps aren't threaded. -- Greg Sullivan, senior product manager for Microsoft
Let's say you want to stream a video clip from YouTube or ESPN. Video streams aren't easily broken down. According to Sullivan, video spools in a serial process, it doesn't easily divide up for multiple cores to work on and then reconvene. As a result, some tasks, like watching a video, will max out one of the cores while the other core or cores update apps in the background, pull in e-mail, and so on.

Chipmaker Nvidia claims that its Tegra 3 processor can efficiently make use of its multiple cores even if the apps themselves aren't threaded.

Either way, all signs point to even better core performance with apps that are specifically designed for multicore use.

Myth No. 4: More cores save battery
Many CNET readers have shared with me their skepticism that more cores will save battery, believing instead that quad-core phones will drain battery faster.
They have a reason to doubt.

The car engine analogy was a favorite with the experts I spoke with. GHz (as in a 1.5GHz processor) are like RPMs, and more processor cores are like more cylinders. More cylinders give you more engine power, but at the cost of guzzling gas. The smartphone's display, CPU (that's the application processor we've been talking about), and the cellular radio suck up the lion's share of the battery. There's a Catch-22 when it comes to performance. Faster CPUs let us accomplish more tasks in a shorter period of time -- rendering images smoother, connecting to the Internet faster -- but they also demand more juice.
It's just like punching the accelerator on the sports car. The faster you do that, the faster you burn through gas. -- Francis Sideco, IHS iSuppli
This increased demand on the battery is why system-level optimization is so important, said Frances Sideco, senior principal analyst of consumer and communications at the analyst firm IHS iSuppli. Engineers on the manufacturer side can be smart about creating software that can help efficiently assign processor tasks.

On top of that, some chips will be inherently more efficient than others (see myth No. 1.) Battery life is an ever-present issue, and the chip-makers that can produce the most battery-balanced systems will see slower battery drain for the same task.

Even with 10 cores, your smartphone's no good to you if it's dead.

Myth No. 5: The CPU stands alone

HTC blew me away with photo rendering in the One X, One S, and One V as quick as they claimed. I mean, it was really, really fast. HTC points to its own image processing chip.
One of the ways that the ARM-based ecosystem is able to optimize the power efficiency is with peripheral side cores -- Francis Sideco, IHS iSuppli
The more you can free up the application cores from having to perform certain resource-heavy tasks, the more they can focus on quickly updating your Facebook status and downloading a podcast. That's why today's system-on-a-chip includes peripheral cores built around the ARM processor, like the graphics processing unit (GPU), any image processors like HTC's, video and audio units for encoding and decoding, and Flash processors. And guess what? The performance of these separate modules all add up to affect the entire system as a whole.

Myth No. 6: Don't forget the operating system

Right now, quad-core mania is centered on the Android OS. The iPhone 4S is dual-core with the next version months away, and Windows Phone OS is currently fixed at single-core.

The potential single core/quad-core divide is a pain point for Microsoft. If consumers think that single-core phones like the Nokia Lumia 900 are slow, they'll view them as inferior. Since CES, Microsoft has leaned hard on its "Smoked by Windows Phone" campaign, which pits a Microsoft employee on a Windows Phone against Android and iPhone users to see whose phone performs simple tasks faster.

Microsoft's point is this: we should evaluate performance based on real-life tasks, and not on theoretical benchmarks.

In the real world, says Microsoft's Sullivan, people listen to music while surfing the Web, and that's something you can do very efficiently with one core. According to Sullivan, performance rests on how efficiently the operating system can manage tasks. Microsoft doesn't actually run multiple apps in the background: it suspends and reactivates them when you actually use the apps, a technique that sucks down less battery, but still lets you pick up where you left off in your browser or map.

With Android, Sullivan adds, you do run multiple threads at the same time, which end up using CPU cycles in the background and can make the entire system less responsive and more unstable while it deals with the simultaneous commands.

Of course, Microsoft's perspective is sure to morph when it starts shipping its own multicore phones. However, Qualcomm's and Samsung VPs, and the IHS iSuppli analyst I spoke with all echoed Sullivan's main sentiment that the way the operating system manages threads of code and processes in general impacts the phone's overall performance, no matter the number of cores.

Myth No. 7: Benchmarks don't lie

Samsung's Nick DiCarlo has a strong opinion about chip performance benchmarks. He explained that most processor performance tests measure dozens of elements of the chip, including subcategories of optimization. Yet, 30 separate and highly specific measurements aren't often useful, especially when manufacturers have a range of chips to report on and compare.
Chip guys...will absolutely show you benchmarks where their chip will dominate everybody else's. -- Nick DiCarlo, Samsung
Aggregating the results with benchmark tools offers a shortcut. Diagnostic apps that calculate benchmark performance for the GPU, CPU, and browser can be useful indicators, but like all statistics, they're also ripe for manipulation.

"Can they be exploited?," DiCarlo offered, "Definitely."

What's to come
The advent of quad-core smartphones in 2012 is inevitable. In 2013, they'll start to become mainstream, as chipmakers like Nvidia and others continue to aggressively push the release cycle and help market the processor a larger part of the purchasing decision.

While I'm just as excited to see ever-faster chips lead to ever more powerful smartphones, it's worth remembering this: quad-core isn't automatically faster in every case, and more isn't always better.

View the original article here

Source From CNET

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