NVIDIA Reveals Kal-El's Fifth "Companion" CPU Core
Over the past seven months or so, NVIDIA has revealed a number of details regarding its upcoming mobile wonder-chip, codenamed Kal-El. According to information provided by NVIDIA dating all the way back to February, Kal-El was to be the world’s first mobile quad-core SoC, sporting an integrated 12-core GeForce GPU, with support for resolutions up to 2560x1600, and performance that’s roughly 5x that of the current Tegra 2.
News out of NVIDIA today, however, reveals that Kal-El actually has 5 CPU cores, four high-performance cores for general processing duties a low-power “companion” core that’ll only be used for background tasks, active standby, and for some music and video playback. NVIDIA is calling this approach Variable Symmetric Multiprocessing, or vSMP.
Kal-El's Low-Power Companion Core
“Our next-generation Tegra processor, codenamed “Project Kal-El,” is widely known as the world’s first quad-core mobile chip. Today, we’re unveiling Kal-El’s little-known fifth core in two new whitepapers that detail its “Variable SMP” architecture.” said NVIDIA’s Matt Wuebbling on a blog post on the company’s website. “This extra core – which we call the “companion core” – runs at a lower frequency and operates at exceptionally low power. During less power-hungry tasks like web reading, music playback and video playback, Kal-El completely powers down its four performance-tuned cores and instead uses its fifth companion core. For higher performance tasks, Kal-El disables its companion core and turns on its four performance cores, one at a time, as the work load increases.”
Core Management, Based On Workload
According to the white papers, the “Companion” core is completely OS transparent, which means the OS and applications are not aware of the core, but they are able to take advantage of it, automatically. Being able to transparently switch between the high-performance cores and low-power Companion core should result in significant power savings. The Companion core uses specialized, low-power transistors that operate at lower frequencies than the high-performance standard cores. However, all five of the cores employ the same ARM Cortex A9 CPU cores. The Companion core is said to operate between 0Mhz (gated, off) and 500MHz, while the performance optimized cores can operate between 0MHz (gated, off) and the SoC’s maximum GHz rating.
NVIDIA’s vSMP technology manages the workload distribution between the Companion and main cores based on the OS and application requirements. The actual management is handled by Kal-El’s Dynamic Voltage and Frequency Scaling (DVFS) feature and CPU Hot-Plug management software and does not require any modifications to the operating system.
According to numbers released by NVIDIA, Kal-El’s unique CPU core configuration and transistor mix give it some marked advantages over competing offerings, both in terms of power and performance. The chart above (provided by NVIDIA) illustrates what we’re referring to—Kal-El is not only the lowest power solution when clocks don’t surpass 1GHz, but its performance is almost double that of current dual-core SoCs, even though Kal-El has twice of the number of CPU cores.