Samsung hopes to make up for previous load-balancing flaws with new fully independent octacore chip

Samsung Electronics Comp., Ltd. (KSC:005930) -- the world's largest smartphone maker -- designs the system-on-a-chip for its smartphones in-house, much like its rival Apple, Inc. (AAPL).  Samsung's chip line -- the Exynos -- has struggled, despite Samsung being a top leader in mobile chip manufacturing (Samsung manufactures Apple's latest and greatest A7, the brains of the iPhone 5S).

I. Exynos 5 Struggles -- is the Third Time the Charm?

The Exynos 5 Dual Core (Exynos 5250) is featured in the Nexus 10 and other products, but it showed surprisingly poor performance, getting beat by Apple's A5X and A6X dual-core chips.  Its successor -- the Exynos 5 Octa Core (Exynos 5410) -- promised to shift that, but was bogged down with cache design issues, which seriously limited the potential of its big.LITTLE core design.

The idea of big,LITTLE was to essentially devote lighter threads to smaller cores, eventually turning on bigger cores as workloads increased.  Thus the Exynos 5 Octa Core uses a mix of four lighter Cortex A7 cores, and four beefy Cortex A15 cores.
Samsung Galaxy S4 wide
Some were disappointed by the performance of the the Galaxy S IV

But because of weirdness with the cache coherency and how Samsung built the early versions of the chip, once the load exceeded the single threaded limit of the lean A7, it transitioned to the A15, and would exclusively use the A15 quad-core cluster until it was saturated, at which point it would use the remaining 3 A7 cores.  In other words if the A7 could hand 0.5 units of work, and the A15 can hand 1.5 units of work, you might expect a workload of three tasks with work (in units) (0.4, 0.2, 0.4) to occupy 3 A7 cores, but instead it occupies an A7 and two A15 cores
Only the least efficient big.LITTLE model -- Cluster Migration -- was supported with the initial octacore Exynos 5.

This "bug", which Samsung never officially addressed significantly impacted performance and power consumption in early units of the Galaxy S4 that shipped with the Exynos Octa Core.

Some believe this is why Samsung primarily shipped the Galaxy S4 with a third-party core -- Qualcomm Inc.'s (QCOM) Snapdragon 600 (quad-core Krait architecture).  An estimated 70 percent of Samsung smartphones shipped with Snapdragon 600s, with the remaining units being powered by the troubled Exynos octacore chips.
The Exynos line has at times disappointed, forcing Samsung to fall back on third-party designs.

A significantly improved Exynos 5 Octa core variant (Exynos 5420) entered mass production in August, fixing much of the load balancing issues and further adding a major bump to the previous model's underpowered GPU (moving from an Imagination Technologies Group Plc.'s (LON:IMG) PowerVR SGX544MP3 (tri-core) to ARM's Mali-T628 MP6, a 6-unit design).

This second-run octacore chip was used in the Galaxy Note 3.

Samsung Galaxy Note 3
Samsung is rumored to have been porting some of the thread balancing improvements in the second generation Exynos 5 Octa back into the first generation model, meaning that newer Galaxy S4s may offer better power performance.

II. Going 64-Bit -- More Than Just Hollow Hype, But a Complex Issue to be Sure

And most recently Korean newspaper IT Today is reporting that development of the Exynos 6 is wrapping up.  Scheduled for production early next year -- reportedly at 14 nm -- the chip may seize the process lead from Intel Corp. (INTC), whose 22 nm LTE-equipped chips are shipping now and will pop up in a slew of products in the January-February window.

Like Intel, Samsung will reportedly use a FinFET 3D transistor design at the 14 nm node.  Samsung paired with International Business Machines Corp. (IBM) and GlobalFoundries to develop this process.  This alliance goes by the name "Common Platform Group".

IBM 14 nm wafer
IBM, GlobalFoundries and Samsung, co-developed the 14 nm FinFET process. [Image Source: PC Mag]

Like the Apple A7, the Exynos 6 will reportedly be 64-bit.  Some may be puzzled at why Samsung and Apple are jumping on this bandwagon.  From a naive approach, the main use of 64-bit registers is to address a larger amount of memory -- typically amounts over the 3 to 4 gigabytes addressable by 32-bit architectures.  Virtually no smartphone has this much memory, so 64-bit capabilities seem wasteful, from a simplistic viewpoint.

To understand why the issue is slightly more complex, you must first start by considering that memory is the primary reason to push for 64-bit adoption -- but in the server space.  

ARM, like Intel and Advanced Micro Devices, Inc. (AMD) before it, has seen the writing on the wall -- most modern server chips need to be 64-bit.  If smartphone and tablet chipmakers jump now to 64-bit (early), by the time 64-bit ARM server chips arrive in late 2014 or early 2015, there will be a growing ecosystem of A64/ARMv8 compatible apps.  This clearly benefits ARM's server ambitions.  And ARM is willing to incentivize smartphone makers to do this, by offering up a more powerful core architecture, packed with more registers to squeeze program data into.

A7 AnandTech
Going to 64-bit brought Apple some nice perks; Samsung's upcoming Exynos 6 SoC should see similar gains. [Image Source: AnandTech]

Due to the nature of the ARM instruction set, the jump from 32-bit ARMv7 (15 registers + 1 program counter) to ARMv8/A64 (31 64-bit registers + 1 program counter) 64-bit also increases the register count.  Realize that register count, of course, is not tied to the width of those registers -- it would have been possible to design a 32 register 32-bit CPU too. However, ARM is deliberately bundling these two design considerations together (as Intel and AMD) have, to further its server gains.

In addition to more registers, ARM is also packing in numerous other exclusive optimizations into its 64-bit instruction set architectures (ISA). The reasoning behind this is because ARM wants to jump into the server space and compete with Intel to power the future cloud computing market.

AnandTech's founder Anand Shimpi explores these issues in more depth in his iPhone 5S review.  But suffice it to say that jumping to 64-bit ARM architectures and instruction sets is about much more than just memory.  ARM Holdings has offered a lot of performance incentives to convince smartphone chipmakers to switch, and the tactic appears to have worked; Apple has a 64-bit chip, and 64-bit chips are approaching the market in the other top ARM chipmakers pipelines (Qualcomm, Samsung, and NVIDIA Corp. (NVDA)).

Back to the 64-bit Exynos 6, it reportedly will use a mix of Cortex-A53 and Cortex-A57 cores from ARM Holdings.  Cache issues have reportedly be fully ironed out, so the cores can be driven independently for optimal load balancing on the lightest applicable collection of cores for a given load.

ARM Cortex A53/A57
The Exynos 6, will reportedly mix A53 and A57 Cortex cores.

The first Exynos 6 chip is expected to possibly pop up in the Galaxy S5, which is expected to launch next spring.  Before that, a minor refresh of the Galaxy S4 (the rumored Galaxy S4 "Advanced") is likely to arrive, potentially bumping the onboard processor to the Exynos 5420, with its more-powerful onboard GPU.

Source: IT Today

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