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Processor designers debate future of multicore

Posted: 08 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:multicore future? CPU designers? processor?

Microprocessor engineers agree multicore designs will be the wave of the future, but they differ widely on how to implement them and surmount the many challenges they pose.

That was the conclusion from a panel discussion at this week's International Solid State Circuits Conference. The panel gathered senior chip designers from AMD, IBM, Intel, Renesas, Sun Microsystems and Tilera.

Chuck Moore, an AMD senior fellow, made the case for the shift to a new software model based on heterogeneous collections of cores optimized for various tasks. He suggested computers should be more like cellphones, using a variety of specialty cores to run modular software scheduled by a high-level applications programming interface.

"We foresee a move from compatibility based on instruction set architecture to compatibility based on an API," said Moore. "You get an order of magnitude better power efficiency by going to heterogeneous cores. Already Microsoft's DirectX APIs tackle a wide variety of graphics processors, so this is a mature software model," he added.

Atsushi Hasegawa, a senior chief engineer at Renesas Technology Corp., generally agreed. He suggested the cellphone's use of many specialty cores working in concert is a good model for future multicore designs.

Brad McCredie, a chief microprocessor engineer at IBM, took the middle ground. He suggested computer processors will go through a phase of experimenting with on-chip accelerators such as the IBM Cell. But ultimately the architectures will narrow down to using to a handful of specialty cores placed next to many general-purpose cores.

Aggressive prediction
Anant Agarwal, founder and CEO of startup Tilera Corp., took the opposing view. He said multicore chips need to be homogenous collections of general-purpose cores to keep the software model simple. However, he was the most aggressive of any of the panelists in his predictions for the growth in the number of cores per socket over the coming decade.

"I would like to call it a corollary of Moore's Law that the number of cores will double every 18 months," said Agarwal, whose company currently ships a 64-core embedded processor.

Agarwal estimated by 2017 embedded processors could sport 4,096 cores, server CPUs might have 512 cores and desktop chips could use 128 cores.

"The question is not whether this will happen but whether we are ready," he said.

Multicore design will deliver a server farm on a chip, shrinking the size of data centers. It could also create desktops that automatically index personal pictures based on facial recognition software, he added.

In Agarwal's view, the industry needs to deliver a new software model because today's operating systems, which use threads and cache coherency snooping, will not scale to such multicore devices. "SMP Linux will go the way of the dinosaur," said Agarwal.

Other panelists were not as aggressive as Agarwal, generally predicting microprocessors will have fewer cores in the next decade.

Sun's stand
Rick Hetherington, chief technologist in Sun Microsystem Inc.'s microelectronics group, suggested servers may have only 32-128 cores by 2018. That's ironic given Sun currently leads the industry in shipping more cores per die than its competitors in computer servers.

Hetherington also suggested today's software model will survive through the next decade. "I think we can support 500 to 1,000 threads per core. In fact, that may even happen in the next five or six years," he said.

Sun's multicore strategy is based in part on handling thread-rich workloads in the rising tide of Web-based applications for giants such as Google Inc. The rise of virtualization in server environments could also fuel Sun's strategy.

McCredie of IBM took issue with Sun's view, suggesting today's servers must run a wide variety of applications, including many non-threaded applications.

"Today's data centers run a big pile of goofy apps where many people don't even know where their source code is anymore," he said. "Google is an exception. We still have discussions about single-threaded apps with customers who may run these applications forever," he added.

Software must evolve
Shekhar Borkar, director of Intel Corp.'s Microprocessor Technology Lab, said microprocessor cores will get increasingly simple, but software needs to evolve more quickly than in the past to catch up.

"A core will look like a NAND gate in the future. You won't want to mess with it," said Borkar. "As for software, the time to market has been long in the past, but we can't afford to let that be the case in the future," he added.

Dave Ditzel, former CPU architect at Sun and founder of Transmeta Corp., agreed. A member of the audience, Ditzel told the panel he helped design Sun's first 64bit CPU then waited nearly 10 years before commercial 64bit OS became available.

"With multicore it's like we are throwing this Hail Mary pass down the field and now we have to run down there as fast as we can to see if we can catch it," Ditzel said.

- Rick Merritt
EE Times

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