The continued increase in microprocessor clock frequency that has come from advancements in fabrication technology and reductions in feature size, creates challenges in maintaining both manufacturing yield rates and long-term reliability of devices. Methods based on defect detection and reduction may not offer a scalable solution due to cost of eliminating contaminants in the manufacturing process and increasing chip complexity. This paper proposes to use the inherent redundancy available in existing and future chip microarchitectures to improve yield and enable graceful performance degradation in fail-in-place systems. We introduce a new yield metric called performance averaged yield (Ypav) which accounts both for fully functional chips and those that exhibit some performance degradation. Our results indicate that at 250nm we are able to increase the Ypav of a uniprocessor with only redundant rows in its caches from a base value of 85% to 98% using microarchitectural redundancy. Given constant chip area, shrinking feature sizes increases fault susceptibility and reduces the base Ypav to 60% at 50nm, which exploiting microarchitectural redundancy then increases to 99.6%.

This paper describes the polymorphous TRIPS architecture that can be configured for different granularities and types of parallelism. The TRIPS architecture is the first in a class of post-RISC, dataflow-like instruction sets called explicit data-graph execution (EDGE). This EDGE ISA is coupled with hardware mechanisms that enable the processing cores and the on-chip memory system to be configured and combined in different modes for instruction, data, or thread-level parallelism. To adapt to small and large-grain concurrency, the TRIPS architecture prototype contains two out-of-order, 16-wide-issue grid processor cores, which can be partitioned when easily extractable fine-grained parallelism exists. This approach to polymorphism provides better performance across a wide range of application types than an approach in which many small processors are aggregated to run workloads with irregular parallelism. Our results show that high performance can be obtained in each of the three modes---ILP, TLP, and DLP---demonstrating the viability of the polymorphous coarse-grained approach for future microprocessors.

The continued increase in microprocessor clock frequency that has come from advancements in fabrication technology and reductions in feature size, creates challenges in maintaining both manufacturing yield rates and long-term reliability of devices. Methods based on defect detection and reduction may not offer a scalable solution due to cost of eliminating contaminants in the manufacturing process and increasing chip complexity. We propose to use the inherent redundancy available in existing and future chip microarchitectures to improve yield and enable graceful performance degradation in fail-in-place systems. We introduce a new yield metric called performance averaged yield (Y/sub PAV/), which accounts both for fully functional chips and those that exhibit some performance degradation. Our results indicate that at 250nm we are able to increase the Y/sub PAV/ of a uniprocessor with only redundant rows in its caches from a base value of 85% to 98% using microarchitectural redundancy. Given constant chip area, shrinking feature sizes increases fault susceptibility and reduces the base Y/sub PAV/ to 60% at 50nm, which exploiting microarchitectural redundancy then increases to 99.6%.

This paper describes the polymorphous TRIPS architecture which can be configured for different granularities and types of parallelism. TRIPS contains mechanisms that enable the processing cores and the on-chip memory system to be configured and combined in different modes for instruction, data, or thread-level parallelism. To adapt to small and large-grain concurrency, the TRIPS architecture contains four out-of-order, 16-wide-issue Grid Processor cores, which can be partitioned when easily extractable fine-grained parallelism exists. This approach to polymorphism provides better performance across a wide range of application types than an approach in which many small processors are aggregated to run workloads with irregular parallelism. Our results show that high performance can be obtained in each of the three modes--ILP, TLP, and DLP-demonstrating the viability of the polymorphous coarse-grained approach for future microprocessors.

The increase in high-performance microprocessor power consumption is due in part to the large power overhead of wide-issue, highly speculative cores. Microarchitectural speculation, such as branch prediction, increases instruction throughput but carries a power burden due to wasted power for mis-speculated instructions. Pipeline over-provisioning supplies excess resources which often go unused. In this paper, we use our detailed performance and power model for an Alpha 21264 to measure both the useful energy and the wasted effort due to mis-speculation and over-provisioning. Our experiments show that flushed instructions account for approximately 6% of total energy, while over-provisioning imposes a tax of 17% on average. These results suggest opportunities for power savings and energy efficiency throughout microprocessor pipelines.

This paper describes several methods for improving the scalability of memory disambiguation hardware for future high ILP processors. As the number of in-flight instructions grows with issue width and pipeline depth, the load/store queues (LSQ) threaten to become a bottleneck in both power and latency. By employing lightweight approximate hashing in hardware with structures called Bloom filters, many improvements to the LSQ are possible. We propose two types of filtering schemes using Bloom filters: search filtering, which uses hashing to reduce both the number of lookups to the LSQ and the number of entries that must be searched, and state filtering, in which the number of entries kept in the LSQs is reduced by coupling address predictors and Bloom filters, permitting smaller queues. We evaluate these techniques for LSQs indexed by both instruction age and the instruction's effective address, and for both centralized and physically partitioned LSQs. We show that search filtering avoids up to 98% of the associative LSQ searches, providing significant power savings and keeping LSQ searches to under one high-frequency clock cycle. We also show that with state filtering, the load queue can be eliminated altogether with only minor reductions n performance for small instruction window machines.

A highly integrated single-chip microprocessor is described that combines a powerful RISC architecture and superscalar machine organization with system design optimizations appropriate for low cost workstation applications. This RISC single-chip (RSC) processor can dispatch up to two instructions per cycle and concurrently execute up to three instructions per cycle. The design integrates a fixed-point execution unit, a floating-point execution unit, an in-page branch unit, an 8-Kbyte unified cache, a memory management unit, a DMA controller, an interrupt controller, ECC on the memory interface, a real-time clock and decrementer, built-in self-test, and a versatile engineering support processor interface on a single die.>

A highly concurrent second-generation RISC (reduced-instruction-set computer) that combines a powerful RISC architecture with sophisticated hardware design techniques to achieve a short cycle time and a low cycles-per-instruction (CPI) ratio is described. Like earlier RISC processors, this design uses a register-oriented instruction set, the CPU is hardwired rather than microcoded, and it features a pipelined implementation. Unlike earlier RISC processors, however, several advanced architectural and implementation features are used, including separate instruction and data caches, zero-cycle branches, multiple-instruction dispatch, and simultaneous execution of fixed- and floating-point instructions. The CPU has a four-word data bus to main memory, a four-word instruction-fetch bus from the I-cache arrays, and a two-word data bus between the D-cache and floating-point unit. The CPU has a full 64-b floating-point engine, and thirty-two 64-b floating point registers in addition to thirty-two 32-b fixed-point registers. In a single cycle, four instructions can be executed simultaneously.>