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alpha 21264 branch predictor

By What does this predictor accomplish that cannot be accomplished with a branch predictor? This strategy is employed in the Alpha 21264. Tournament Branch Predictor Used in Alpha 21264: Track both “local” and global history Intended for mixed types of applications Global history: T/NT history of past k branches, The Alpha 21264 and Alpha EV8 microprocessors used a fast single-cycle next-line predictor to handle the branch target recurrence and provide a simple and fast branch prediction. Papers, Feb. 1997,,pp. • The second branch predictor, which is slower, more complicated, and with bigger tables, will override a possibly wrong prediction made by the first predictor. Tournament Predictor in Alpha 21264 1. So one of the interesting things going back to this two level branch predictor, is sometimes, you want per branch information or per branch history. Global predictor (GAg): – 4K entries, indexed by the history of the last 12 branches; each entry in the global predictor is a standard 2-bit predictor – 12-bit pattern: ith bit 0 => ith prior branch … The Alpha 21264 and Alpha EV8 microprocessors used a fast single-cycle next line predictor to handle the branch target recurrence and provide a simple and fast branch prediction. Combine branch predictors • local, per-branch prediction, accessed by the PC • correlated prediction based on the last m branches, assessed by ... • tournament branch prediction • Alpha 21264 has a combination of local (1K entries, 10 history bits) & global (4K entries) predictors When a line prediction is overridden, the Alpha predictor incurs a single-cycle penalty, which is small compared to the 7-cycle penalty for a branch misprediction. The local predictor. The design decisions for the TRIPS prototype predictor were made based on results from the Trimaran hyperblock-TRIPS simulator infrastructure. This predictor was used as the Alpha 21264 has a minimum branch … Because the hardware chooses between the better of two predictors at each point, it is called a tournament predictor. IBM Power 4, Alpha 21264 1101 01 10 GAp BHR PC 1001 10 01 1010 BHR PC 1001 gshare BHR PC 1101 0110 XOR 1011 BHR PC 1001 1010 XOR 0011 0000 0001 0010 ... • Used in Alpha EV8 (ultimately cancelled) • P. Michaud, A. Seznec 20 Branch Target Prediction • In addition to predicting the branch direction, we must Describe the benefits of a trace cache in terms of energy consumption of the processor? 18-447 Computer Architecture Lecture 10: Branch Handling and Branch Prediction (II) Prof. Onur Mutlu Carnegie Mellon University Spring 2014, 2/5/2014. Combining Branch Predictors. Local predictor maintains the per-branch history and each entry is 2-bit saturation counter. TN-36, Digital Equipment Corporation Western Research Laboratory, June 1993. Perhaps the best known examples, at the time of writing, are the Pentium Pro [Gwennap and Alpha 21264 [Gwennap96]. Better answers Decomposed SPEC95 Applications 0% 50% 100% 150% 200% 250% Turb3d Swm256 Tomcatv 1T 2T 3T 4T. The property of local correlation implies branch direction prediction on the basis of the branch's past behavior. 16 Branch Target Prediction •In addition to predicting the branch direction, we must Dig. 4K 2-bit counters to choose from among a global predictor and a local predictor 2. “A 600 Mhz Superscalar RISC,Microprocessor With Out-of-Order Execution”, IEEE Int.,Solid-State Circuits Conf. Predictor Branch PC Table of 2-bit saturating counters Local Predictor Global Predictor M U X Alpha 21264: 1K entries in level-1 1K entries in level-2 4K entries 12-bit global history 4K entries Total capacity: ? 25 • The first branch predictor is fast and simple. 3. The 21264 implemented the Alpha instruction set architecture (ISA). The second branch predictor, which is slower, more complicated, and with bigger tables, will override a possibly wrong prediction made by the first predictor. The Alpha 21264 contains a line predictor in its fetch engine. 176-177.,[Lei97] Daniel Leibholz and Rahul Razdan, “The Alpha,21264: A 500 Mhz Out-of-Order Execution,Microprocessor”, Proceedings of IEEE COMPCON ’97,,pp. There are total 1 The Alpha 21264 branch predictor uses local history and glob-al history to predict future branch directions since branches exhib-it both local correlation and global correlation. Improved Branch Predictors. Az Alpha 21264 mag, amelyen az Alpha 21364 alapult, úgy volt tervezve, hogy egy külső, kereskedelemben kapható SRAM-ból felépülő gyorsítótárat használjon, amelynek jelentősen nagyobb a latenciája, mint az Alpha 21364 lapkára integrált Scache egységének. More details and comparison with multiple branch prediction approaches can be found in [18]. Branch predictor overrides and trains fetch predictor I-cache Fetch Decode/REN Branch Predictor Fetch Predictor Out … Alpha 21264 Alpha 21264 Microprocessor Product Brief The Alpha 21264 microprocessor, with benchmarks over 30 SPECint95 and 50 SPECfp95, and with spectacular bandwidths over 3.2 GB/s for L2 cache and over 2.6 GB/s for memory, enables the system designer to produce the highest performance systems ranging from PC clients to enterprise servers. 18-740/640 Computer Architecture Lecture 5: Advanced Branch Prediction Prof. Onur Mutlu Carnegie Mellon University Fall 2015, 9/16/2015 branch predictors have been incorporated in several rcccnt high-performance microprocessors. The DEC Alpha 21264 (EV6) uses a next-line predictor overridden by a combined local predictor and global predictor, where the combining choice is made by a bimodal predictor. Cache 64KB 2-Set Exec Exec Reg Exec File (80) FP Issue Queue (15) Reg File (72) REK August 1998 4 Int Issue Queue (20) FP Issue Queue (15) Alpha 21264: Block Diagram Cache Bus Phys Addr FETCH MAP QUEUE REG EXEC DCACHE Alpha 21264 Last updated March 08, 2019 Alpha 21264 microarchitecture. Explain the purpose of this predictor. So. Branch predictor. And, this brings us to tournament predictors. View online or download Compaq Alpha 21264 Hardware Reference Manual Cache 64KB 2-Set Exec Exec Reg Exec File (80) FP Issue Queue (15) Reg File (72) REK August 1998 4 Int Issue Issue Queue (15) Alpha 21264: Block Diagram FETCH MAP QUEUE REG EXEC 5 6 -Reg 4 Instructions / cycle) Sys Bus 64-bit 128-bit 44 Buffer 64KB 2 … However, for the TRIPS Ezáltal az … The algorithm was developed by Scott McFarling at Digital's Western Research Laboratory (WRL) and was described in a 1993 paper. 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