The Value Of Multi-Core Processors On Phones

We all know the value of symmetric multiprocessing (SMP) on our PC's. At any given time, a modern desktop can have 50-100 process running from the browser or RSS reader you are using to read this to dozens of background tasks indexing files, checking your email, looking for keywords on Twitter and more. Your phone can benefit from SMP as well, but for entirely different reasons.It is doubtful that any phone will have 50 processes running at once in the near future, but neither do modern smartphones have one process either. Even if your phone doesn't support third party multitasking (Apple iPhone, Windows Phone 7), it does multitask. The reason Apple has given for not allowing third party multitasking is power consumption. The more open processes there are, the busier the processor is, so the more power it must use to juggle everything.

Another reason is device stability. Windows Mobile phones have supported multitasking since their inception. You can definitely feel the device slow to a crawl as more and more apps are open. Part of this is the app developer's fault by not adequately testing how their app will perform in the background and ensure that it doesn't take over the phone. Part of this though is Microsoft's fault. During the design of the Pocket PC interface, which has morphed into Windows Mobile 6.5, MS designers were adamant that there be no close button. The user should not have to deal with that, so instead the OS would monitor resources (this is another process by the way) and close the oldest background app as necessary. While MS went so far at one time to deny the "Windows Mobile" certification logo for apps that dared include an "Exit" item on the menu, they later relaxed that. Ultimately though, the OS, and not the user, was in control. That worked so well for the software giant that they banned third party multitasking altogether with the new platform. Sluggish performance and rogue apps hogging the processor made the device unusable until you either waited for everything to settle down or you just popped the soft reset button.

Enter SMP. Qualcomm recently announced their multi-core Snapdragon line of processors, but they aren't the only one in the mobile SMP game. I had a chance last week to talk to Robert Tolbert of the OMAP 4 platform team at Texas Instruments. Most Nokia smartphones, the Palm Pre, Motorola Droid and hundreds of other phones have an OMAP chip inside, likely an OMAP 3. Their new OMAP 4 line is based on the ARM Cortex A9 architecture and was unveiled in February of this year. It should be in handsets for sale in early 2011.

These dual core systems do more than make things go faster. In fact, in talking with Mr. Tolbert, I got the impression that raw performance wasn't the primary goal. Power conservation has to be a top priority of any mobile device, especially phones. It may seem counter intuitive, but multi-core chips can deliver equivalent performance of single core chips but with less power consumption.

All processors suffer from power leakage, which is the power that is consumed by unused circuitry. So for a mobile processor, a 2GHz chip has more circuitry, or overhead, than dual core 1GHz chips would have. If your phone is doing nothing, or maybe just playing music, it could simply turn off the second core. Now you are getting equivalent performance of a more powerful single core chip but with far less power consumption. Mr. Tolbert estimated the single core chips may consume 50%-100% more power than a dual core chip for the same tasks.

Other benefits are more obvious. With modern apps, each process can be split into multiple threads, so opening your browser is one process but has multiple threads to your browsing tasks, such as rendering different parts of the web page. A single core chip can only handle one thing at a time but a dual core can double the throughput. (Let's ignore hyper-threading and other virtualization technologies for now.)

If the OS is able to control which core processes run on, it could delegate one core to primarily handle the OS itself, from the phone to built in apps like the browser or Exchange ActiveSync connector. The second core could be used to handle third party apps, or at least background processes. This may pave the way for the rebirth of true third party multitasking in platforms that currently deny it. For the record, iOS 4 does not support true third party multitasking. As long as the app and OS are SMP aware, benefits can range from modest to drastic.

So what mobile phones are SMP aware? Right now, Android certainly does given its Linux core. That doesn't mean though that the Android team doesn't have some tweaking to do when multi-core chips ship. So far, there hasn't been any real reason to optimize for SMP phones. Nokia is working on it and will be ready when the OMAP 4 line ships. Windows CE, now renamed to Windows Embedded Compact 7, is SMP aware but when I reached out to Microsoft to see if Windows Phone 7, which is based on WEC7, would be SMP aware when it shipped, they didn't return calls to comment.

TI has made a white paper available entitled "Leverage the Benefits of Symmetric Multiprocessing (SMP) in Mobile Devices." That can give you far more details on TI's vision of how SMP benefits mobile devices, most of which would match the vision of their competitors. Starting this fall or winter, start looking for dual core specs in the rumor mill of phones rather than single core MHz specs. You should get more bang for the buck. Speaking of bucks, what about the cost? Mr. Tolbert couldn't give specifics, but did say that the cost (both price and size) of an OMAP 4 processor could be had for the same cost as an OMAP 3 processor three years ago. Just like everything else in the computer world, smaller, cheaper, faster and more efficient.

Quad-core anyone?