Dennard scaling ended a decade ago. Energy reduction by lowering supply voltage has been limited because of guard bands and a subthreshold slope of over 60mV/decade in MOSFETs. On the other hand, newly-proposed logic devices maintain a high on/off ratio for drain currents even at significantly lower operating voltages. However, such ultra low power technology would eventually suffer from intermittent errors in logic as a result of operating close to the thermal noise floor. Computational error correction mitigates this issue by efficiently correcting stochastic bit errors that may occur in computational logic operating at low signal energies, thereby allowing for energy reduction by lowering supply voltage to tens of millivolts. Cores based on a Redundant Residual Number System (RRNS), which represents a number using a tuple of smaller numbers, are a promising candidate for implementing energyefficient computational error correction. However, prior RRNS core microarchitectures abstract away the memory hierarchy and do not consider the power-performance impact of RNS-based memory addressing. When compared with a non-error-correcting core addressing memory in binary, naive RNS-based memory addressing schemes cause a slowdown of over 3x/2x for inorder/out-of-order cores respectively. In this paper, we analyze RNS-based memory access pattern behavior and provide solutions in the form of novel schemes and the resulting design space exploration, thereby, extending and enabling a tangible, ultra low power RRNS based architecture.

Dennard scaling has ended. Lowering the voltage supply ( V dd ) to sub-volt levels causes intermittent losses in signal integrity, rendering further scaling (down) no longer acceptable as a means to lower the power required by a processor core. However, it is possible to correct the occasional errors caused due to lower V dd in an efficient manner and effectively lower power. By deploying the right amount and kind of redundancy, we can strike a balance between overhead incurred in achieving reliability and energy savings realized by permitting lower V dd . One promising approach is the Redundant Residue Number System (RRNS) representation. Unlike other error correcting codes, RRNS has the important property of being closed under addition, subtraction and multiplication, thus enabling computational error correction at a fraction of an overhead compared to conventional approaches. We use the RRNS scheme to design a Computationally-Redundant, Energy-Efficient core, including the microarchitecture, Instruction Set Architecture (ISA) and RRNS centered algorithms. From the simulation results, this RRNS system can reduce the energy-delay-product by about 3× for multiplication intensive workloads and by about 2× in general, when compared to a non-error-correcting binary core.

Parallel programs can be characterized by task graphs encoding instructions, memory accesses, and the parallel work’s dependencies, while representing any threading library and architecture. This article presents Contech, a high performance framework for generating dynamic task graphs from arbitrary parallel programs, and a novel representation enabling programmers and compiler optimizations to understand and exploit program aspects. The Contech framework supports a variety of languages (including C, C++, and Fortran), parallelization libraries, and ISAs (including × 86 and ARM). Running natively for collection speed and minimizing program perturbation, the instrumentation shows 4 × improvement over a Pin-based implementation on PARSEC and NAS benchmarks.

As more heterogeneous architecture solutions continue to emerge, coherence solutions tailored for these architectures will become mandatory. Coherence hierarchies will likely continue to be prevalent in future large-scale shared memory architectures. However, past experience has shown that hierarchical coherence protocol design is a non-trivial problem, especially when considering the verification effort required to guarantee correctness. While some strategies do exist for verification of homogenous coherence hierarchies, support for reasonable verification of heterogeneous coherence hierarchies is currently unavailable. Ideally, hierarchical coherence protocols composed of `building block' protocols should be able to take advantage of incremental verification to side step the state-space explosion problem which hampers any large-scale verification effort. In this work, we prove this can be accomplished through the use of the Manager-Client Pairing (MCP) framework, which provides encapsulation and permission checking support that enables a form of state-space symmetry. When combined with an inductive proof, this ensures the validation properties of proper permission distribution and livelock/deadlock freedom are enforced by any hierarchical composition of MCP compliant protocols. Demonstration of this methodology through the MurPhi formal verifier shows several orders of magnitude improvement in verification cost compared to full hierarchy verification.