We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.

Device Requirements for Optical Interconnects to Silicon Chips

This paper presents the many-core architecture, with hundreds to thousands of small cores, to deliver unprecedented compute performance in an affordable power envelope. We discuss fine grain power management, memory bandwidth, on die networks, and system resiliency for the many-core system.

http://www.ee.unlv.edu/~meiyang/ecg700/readings/Thousand%20Core%20Chips%20A%20Technology%20Perspective.pdf

Thousand core chips: a technology perspective

Commodity computer systems contain more and more processor cores and exhibit increasingly diverse architectural tradeoffs, including memory hierarchies, interconnects, instruction sets and variants, and IO configurations. Previous high-performance computing systems have scaled in specific cases, but the dynamic nature of modern client and server workloads, coupled with the impossibility of statically optimizing an OS for all workloads and hardware variants pose serious challenges for operating system structures.We argue that the challenge of future multicore hardware is best met by embracing the networked nature of the machine, rethinking OS architecture using ideas from distributed systems. We investigate a new OS structure, the multikernel, that treats the machine as a network of independent cores, assumes no inter-core sharing at the lowest level, and moves traditional OS functionality to a distributed system of processes that communicate via message-passing.We have implemented a multikernel OS to show that the approach is promising, and we describe how traditional scalability problems for operating systems (such as memory management) can be effectively recast using messages and can exploit insights from distributed systems and networking. An evaluation of our prototype on multicore systems shows that, even on present-day machines, the performance of a multikernel is comparable with a conventional OS, and can scale better to support future hardware.

/pdf/the-multikernel-a-new-os-architecture-for-scalable-multicore-1zaxph0v39.pdf

The multikernel: a new OS architecture for scalable multicore systems

The design and performance of next-generation chip multiprocessors (CMPs) will be bound by the limited amount of power that can be dissipated on a single die We present photonic networks-on-chip (NoC) as a solution to reduce the impact of intra-chip and off-chip communication on the overall power budget A photonic interconnection network can deliver higher bandwidth and lower latencies with significantly lower power dissipation We explain why on-chip photonic communication has recently become a feasible opportunity and explore the challenges that need to be addressed to realize its implementation We introduce a novel hybrid micro-architecture for NoCs combining a broadband photonic circuit-switched network with an electronic overlay packet-switched control network We address the critical design issues including: topology, routing algorithms, deadlock avoidance, and path-setup/tear-down procedures We present experimental results obtained with POINTS, an event-driven simulator specifically developed to analyze the proposed idea, as well as a comparative power analysis of a photonic versus an electronic NoC Overall, these results confirm the unique benefits for future generations of CMPs that can be achieved by bringing optics into the chip in the form of photonic NoCs

/pdf/photonic-networks-on-chip-for-future-generations-of-chip-4wqloco96y.pdf

Photonic Networks-on-Chip for Future Generations of Chip Multiprocessors

As industry moves towards many-core chips, networks-on-chip (NoCs) are emerging as the scalable fabric for interconnecting the cores. With power now the first-order design constraint, early-stage estimation of NoC power has become crucially important. ORION [29] was amongst the first NoC power models released, and has since been fairly widely used for early-stage power estimation of NoCs. However, when validated against recent NoC prototypes -- the Intel 80-core Teraflops chip and the Intel Scalable Communications Core (SCC) chip -- we saw significant deviation that can lead to erroneous NoC design choices. This prompted our development of ORION 2.0, an extensive enhancement of the original ORION models which includes completely new subcomponent power models, area models, as well as improved and updated technology models. Validation against the two Intel chips confirms a substantial improvement in accuracy over the original ORION. A case study with these power models plugged within the COSI-OCC NoC design space exploration tool [23] confirms the need for, and value of, accurate early-stage NoC power estimation. To ensure the longevity of ORION 2.0, we will be releasing it wrapped within a semi-automated flow that automatically updates its models as new technology files become available.

/pdf/orion-2-0-a-fast-and-accurate-noc-power-and-area-model-for-3pivncxvm6.pdf

ORION 2.0: a fast and accurate NoC power and area model for early-stage design space exploration

A 275mm2 network-on-chip architecture contains 80 tiles arranged as a 10 times 8 2D array of floating-point cores and packet-switched routers, operating at 4GHz. The 15-F04 design employs mesochronous clocking, fine-grained clock gating, dynamic sleep transistors, and body-bias techniques. The 65nm 100M transistor die is designed to achieve a peak performance of 1.0TFLOPS at 1V while dissipating 98W.

An 80-Tile 1.28TFLOPS Network-on-Chip in 65nm CMOS

A multicore processor in 65-Nm technology with 80 single-precision, floatingpoint cores delivers performance in excess of a Teraflops while consuming less than 100 W. A 2D on-die mesh interconnection network operating at 5 GHz provides the high-performance communication fabric to connect the cores. The network delivers a bisection bandwidth of 2.56 Terabits per second and a per hop fall-through latency of 1 nanosecond.

A 5-GHz Mesh Interconnect for a Teraflops Processor

This paper describes an integrated network-on-chip architecture containing 80 tiles arranged as an 8x10 2-D array of floating-point cores and packet-switched routers, both designed to operate at 4 GHz. Each tile has two pipelined single-precision floating-point multiply accumulators (FPMAC) which feature a single-cycle accumulation loop for high throughput. The on-chip 2-D mesh network provides a bisection bandwidth of 2 Terabits/s. The 15-FO4 design employs mesochronous clocking, fine-grained clock gating, dynamic sleep transistors, and body-bias techniques. In a 65-nm eight-metal CMOS process, the 275 mm2 custom design contains 100 M transistors. The fully functional first silicon achieves over 1.0 TFLOPS of performance on a range of benchmarks while dissipating 97 W at 4.27 GHz and 1.07 V supply.

An 80-Tile Sub-100-W TeraFLOPS Processor in 65-nm CMOS

A five-port two-lane pipelined packet-switched router core with phase-tolerant mesochronous links forms the key communication fabric for an 80-tile network-on-chip (NoC) architecture. The 15FO4 design combines 102 GB/s of raw bandwidth with low fall-through latency of 980 ps. A shared crossbar architecture with a double-pumped crossbar switch enables a compact 0.34 mm2 router layout. In a 65nm eight-metal CMOS process, the router contains 210K transistors and operates at 5.1GHz at 1.2 V, while dissipating 945 mW.

A 5.1GHz 0.34mm 2 Router for Network-on-Chip Applications

The Pentium/spl reg/ 4 processor architecture uses a 2/spl times/ frequency core clock to implement low latency integer operations. Low-voltage-swing (LVS) logic circuits implemented in 90-nm technology meet the frequency demands of a third-generation integer-core design.

A. Singh

Papers

An 80-Tile 1.28TFLOPS Network-on-Chip in 65nm CMOS

A 5-GHz Mesh Interconnect for a Teraflops Processor

An 80-Tile Sub-100-W TeraFLOPS Processor in 65-nm CMOS

A 5.1GHz 0.34mm 2 Router for Network-on-Chip Applications

Low-voltage swing logic circuits for a Pentium/spl reg/ 4 processor integer core