Leveraging Optical Technology in Future Busbased Chip Multiprocessors
Leveraging Optical Technology in Future Bus-based Chip Multiprocessors Kevin Kane EEL 6905 1/25/07
Content n n n Background Introduction to paper Optical Technology Overview n n Opto-electric Bus Architecture n n n Transmitter Waveguide Receiver Bus design Estimations Simulated Design Evaluation Results and Conclusions Future Research
Background n n n Optical technology (like 3 D integration) may solve current limitations in chip-tochip communications. Ten years ago electrical-optical translation costs and CMOS incompatibility seemed insurmountable. Benefits include: n high speed, high bandwidth, low-chip power, good electrical isolation, low electrometric inference
Introduction to Paper Computer Systems Laboratory Cornell University http: //csl. cornell. edu/ n “Investigate the potential of optical technology as a low-latency, highbandwidth shared bus supporting snoopy cache coherence in future CMP. ”
C. M. P. n Chip Multi. Processor (CMP) is symmetric multiprocessing (SMP) implemented on a single VLSI integrated circuit. Multiple processor cores (multicore) typically share a common second- or third-level cache and interconnect. - Wikipedia -
Snooping? n Bus snooping is a technique used in distributed shared memory systems and multiprocessors aimed at achieving cache coherence. Every cache controller monitors the bus, awaiting for broadcasts which may cause it to invalidate its cache line. - Wikipedia -
W. D. M. n Wavelength-Division Multiplexing (WDM) technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over one strand of fiber. - Wikipedia -
Optical Technology Overview n “on-chip modulator-based optical transmission” n n n Transmitter Waveguide Receiver
Transmitter n Optical transmission requires: n n n Laser source (on-chip and off chip) Modulator driver (electrical) circuit
Waveguide n n Silicon (Si) vs. polymer (? ) Silicon in this paper
Receiver n Optical-to-electrical conversion n n Photodetector and trans-impedance amplifier WDM applications require a wave-selective filter
Opto-Electrical Bus Architecture n n n 32 nm process technology Die Area: 400 mm sq. 4 “Cores” n n Three levels of cache n n 4 GHz frequency 16 L 2 caches split among cores Optical bus n n “…look-like structure, …” Bus for a total of b address, data, and snoop response bits w wavelengths Multiplex-by-node organization
Simple 4 -core CMP Scheme
Optical Bus Topology Characteristics (results) # of nodes n Topology determines: n n n Frequency Area Power address wavelengths per node data wavelengths per node H-nxk. Ak. D
Two Cache Configurations 16 X 256 KB L 2 vs. 16 X 256 KB L 2
Electrical Networks (baseline)
Electrical Topology Characteristics (results) n Two possible topologies determine: n Area n Power
Applications (benchmark) Using MIPS binaries compiled with –O 3 optimization level
Results and Conclusions
Average Number of Bus Requests
Performance improvement
Latency
The Basic Point! “Indeed, for the configurations under study, the main overall benefits come from reduced contention (and thus effective latency) for data transfers. Our simulations show that the data network struggles to supply the bandwidth needed to satisfy these requests. It is in the data network that the availability of extra wavelengths through WDM yields the largest performance improvements. ”
Parallel Efficiencies n Scalability improves with the addition of optical technology
Results n n n Optical technology in bus-based CMPs can have a positive impact on performance. WDM can come at very small additional area and power consumption. Performance gains from the opto-electric buses could be given back in exchange for power/area savings
Future Research n n Best use of optical waveguides and WDM for a particular CMP design Polymer waveguides vs. Silicon waveguides n n Hybrid system Further penetrations into the bus protocol Optical module sensitivity to temperatures variations n n n Polymer (fast but low bandwidth) Silicon (high bandwidth but slow)
Thank you
- Slides: 27