Let’s take a look at each of these predictors in more detail. 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. Branch predictor-Wikipedia The property of local correlation implies branch direction prediction on the basis of the branch’s past behavior. Dig. Local-history predictors are typi- 4K 2-bit counters to choose from among a global predictor and a local predictor 2. Describe the benefits of a trace cache in terms of energy consumption of the processor? The property of local correlation implies branch direction prediction on the basis of the branch's past behavior. “A 600 Mhz Superscalar RISC,Microprocessor With Out-of-Order Execution”, IEEE Int.,Solid-State Circuits Conf. 20 “Real” Branch Predictors • Alpha 21264 – 8-stage pipeline, mispredict penalty 7 cycles – 64 KB, 2-way instruction cache with line and way prediction bits (Fetch) • Each 4-instruction fetch block contains a prediction for the next fetch block – Hybrid predictor (Fetch) • 12-bit GAg (4K-entry PHT, 2 bit counters) • 10-bit PAg (1K-entry BHT, 1K-entry PHT, 3-bit counters) 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 Alpha 21264 uses this kind of branch predictor, with a slower hybrid branch predictor overriding a less accurate but faster line predictor [18]. Perhaps the best known examples, at the time of writing, are the Pentium Pro [Gwennap and Alpha 21264 [Gwennap96]. The Alpha 21264 is a Digital Equipment Corporation RISC microprocessor introduced in October, 1996. 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. design was similar in structure to the Alpha 21264 branch predictor [10]. • Used in e.g. It's great name. The second branch predictor, which is slower, more complicated, and with bigger tables, will override a possibly wrong prediction made by the first predictor. Branch Predictors Next-Line Address L1 Ins. Improved Branch Predictors. The Alpha 21264 branch predictor uses local history and global history to predict future branch directions since branches exhibit both local correlation and global correlation. Tech. Local predictor maintains the per-branch history and each entry is 2-bit saturation counter. 25 1. More details and comparison with multiple branch prediction approaches can be found in [18]. There are total 1 This predictor was used as the Alpha 21264 has a minimum branch … Alpha 21264 Tournament Predictor Minimum branch penalty: 7 cycles Typical branch penalty: 11+ cycles 48K bits of target addresses stored in I-cache Predictor tables are reset on a context switch Kessler, “The Alpha 21264 Microprocessor,” IEEE Micro 1999. This strategy is employed in the Alpha 21264. 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 Because the hardware chooses between the better of two predictors at each point, it is called a tournament predictor. 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. The design decisions for the TRIPS prototype predictor were made based on results from the Trimaran hyperblock-TRIPS simulator infrastructure. 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. Alpha 21264 Last updated March 08, 2019 Alpha 21264 microarchitecture. 18-447 Computer Architecture Lecture 10: Branch Handling and Branch Prediction (II) Prof. Onur Mutlu Carnegie Mellon University Spring 2014, 2/5/2014. 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: ? This predictor was used as the Alpha 21264 has a minimum branch misprediction penalty of seven cycles ... and the instruction queues, the average branch … 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: ? 18-740/640 Computer Architecture Lecture 5: Advanced Branch Prediction Prof. Onur Mutlu Carnegie Mellon University Fall 2015, 9/16/2015 By • The first branch predictor is fast and simple. 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 … This strategy is employed in the Alpha 21264. Compaq Alpha 21264 Pdf User Manuals. Better answers Multithreaded Applications 0% 50% 100% 150% 200% 250% 300% The local predictor. Branch Predictors Next-Line Address L1 Ins. What does this predictor accomplish that cannot be accomplished with a branch predictor? The Alpha 21264 contains a line predictor in its fetch engine. Branch predictor. TN-36, Digital Equipment Corporation Western Research Laboratory, June 1993. And, this brings us to tournament predictors. 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. View online or download Compaq Alpha 21264 Hardware Reference Manual Better answers Multiprogrammed workload 0% 50% 100% 150% 200% 250% t P P 1T 2T 3T 4T. Alpha 21264.1 —We introduce a version of the perceptron predictor that uses both global and per-branch information, yielding misprediction rates that are 14% more Among two-level predictors, those using global history The second branch predictor, which is slower, more complicated, and with bigger tables, will override a possibly wrong prediction made by the first predictor. 3. So. However, for the TRIPS branch predictors have been incorporated in several rcccnt high-performance microprocessors. • The second branch predictor, which is slower, more complicated, and with bigger tables, will override a possibly wrong prediction made by the first predictor. Papers, Feb. 1997,,pp. Branch predictor overrides and trains fetch predictor I-cache Fetch Decode/REN Branch Predictor Fetch Predictor Out … Tournament Predictor in Alpha 21264 1. 20 Branch Target Prediction • In addition to predicting the branch direction, we must Because the hardware chooses between the better of two predictors at each point, it is called a tournament predictor. The 21264 implemented the Alpha instruction set architecture (ISA). Explain the purpose of this 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 Branch prediction is performed by a tournament branch prediction algorithm. 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, 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. Ezáltal az … 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. Alpha 21264 Branch Predictors Similar to POWER4 Alpha 21264 branch predictor is also composed of three units – Local predictor, Global predictor, and Choice predictor. 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. 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. Combining Branch Predictors. It came up first in the, ALPHA 21264 and what they did is they actually had predictors, to predict which predictor to use. 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 … The algorithm was developed by Scott McFarling at Digital's Western Research Laboratory (WRL) and was described in a 1993 paper. Better answers Decomposed SPEC95 Applications 0% 50% 100% 150% 200% 250% Turb3d Swm256 Tomcatv 1T 2T 3T 4T. 16 Branch Target Prediction •In addition to predicting the branch direction, we must Design was similar in structure to the Alpha 21264 contains a line predictor in its fetch engine prediction can! 'S past behavior and comparison with multiple branch prediction approaches can be in! Describe the benefits of a trace cache in terms of energy consumption of the branch direction we... Decomposed SPEC95 Applications 0 % 50 % 100 % 150 % 200 % 250 Turb3d. 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