Integrating more processor cores on-die has become the unanimous trend in the microprocessor industry. Most of the current research thrusts using chip multiprocessors (CMPs) as the baseline to analyze problems in various domains. One of the main design issues facing CMP systems is the growing number of snoops required to maintain cache coherency and to support self/cross-modifying code that leads to power and performance limitations. In this paper, we analyze the internal and external snoop behavior in a CMP system and relax the snoopy cache coherence protocol based on the program semantics and properties of the shared variables for saving power. Based on the observations and analyses, we propose two novel techniques: Selective Snoop Probe (SSP) and Essential Snoop Probe (ESP) to reduce power without compromising performance. Our simulation results show that using the SSPtechnique, 5% to 65% data cache energy savings per core for different processor configurations can be achieved with 1% to 2% performance improvement. We also show that 5% to 82% of data cache energy per core is spent on the non-essential snoop probes that can be saved using the ESP technique.

This paper presents the first multiobjective microarchitectural floorplanning algorithm for high-performance processors implemented in two-dimensional (2-D) and three-dimensional (3-D) ICs. The floorplanner takes a microarchitectural netlist and determines the dimension as well as the placement of the functional modules into single- or multiple-device layers while simultaneously achieving high performance and thermal reliability. The traditional design objectives such as area and wirelength are also considered. The 3-D floorplanning algorithm considers the following 3-D-specific issues: vertical overlap optimization and bonding-aware layer partitioning. The hybrid floorplanning approach combines linear programming and simulated annealing, which is shown to be very effective in obtaining high-quality solutions in a short runtime under multiobjective goals. This paper provides comprehensive experimental results on making tradeoffs among performance, thermal, area, and wirelength for both 2-D and 3-D ICs

The Translation Look-aside Buffer (TLB), a content addressable memory, consumes significant power due to the associative search mechanism it uses in the virtual to physical address translation. Based on our analysis of the TLB accesses, we make two observations. First, the entropy or information content of the stack virtual page numbers is low due to high spatial locality of stack memory references. Second, the entropy of the higher order bits of global memory references is low since the size of the global data is determined and fixed during compilation of a program. Based on these two characteristics, we propose two techniques: an entropy-based speculative stack address TLB and a deterministic global address TLB to achieve energy reducing. Our results show an average of 47% energy savings in the data TLB with less than 1%overall performance impact.

In this paper, we present the first multi-objective microarchitectural floorplanning algorithm for designing highperformance, high-reliability processors in the early design phase. Our floorplanner takes a microarchitectural netlist and determines the placement of the functional modules while simultaneously optimizing for performance and thermal reliability. The traditional design objectives such as area and wirelength are also considered. Our multi-objective hybrid floorplanning approach combining Linear Programming and Simulated Annealing is shown to be fast and effective in obtaining high-quality solutions. We evaluate the trade-off of performance, temperature, area, and wirelength and provide comprehensive experimental results.

Modern processors can issue and execute multiple instructions per cycle, often performing multiple memory operations simultaneously. To reduce stalls due to resource conflicts, most processors employ multi-ported L1 caches and TLBs to enable concurrent memory accesses. In this paper, we observe that data TLB lookups within a cycle and across consecutive cycles are often synonymous --- they go to the same page. To exploit this finding, we propose two new mechanisms --- intra-cycle compaction and inter-cycle compaction of address translation requests in order to save energy in the data TLB. Our results show that average energy savings of 27% using intra-cycle, 42% using inter-cycle in a conventional d-TLB, and 56% using inter-cycle compaction in semantic-aware d-TLBs can be achieved. When these 2 compaction techniques are combined together and applied to both the i-TLB and semantic-aware d-TLBs, an average energy savings of 76% (up to 87%) is obtained

The memory subsystem, including address translations and cache accesses, consumes a major portion of the overall energy on a processor. In this paper, we address the memory energy issues by using a streamlined architectural partitioning technique that effectively reduces energy consumption in the memory subsystem without compromising performance. It is achieved by decoupling the d-TLB lookups and the data cache accesses, based on the semantic regions defined by programming languages and software convention, into discrete reference substreams --- stack, global static, and heap. Their unique access behaviors and locality characteristics are analyzed and exploited for power reduction. Our results show that an average of 35% energy can be reduced in the d-TLB and the data cache. Furthermore, an average of 46% energy can be saved by selectively multi-porting the semantic-aware d-TLBs and data caches against their monolithic counterparts.