A 2bcgskew Fused by a RHSP Veerle Desmet Hans Vandierendonck Koen De Bosschere Ghent University Member HiPEAC
1st JILP Championship Branch Prediction (CBP-1) --- December 5, A 2bcgskew Fused by a RHSP
1st JILP Championship Branch Prediction (CBP-1) --- December 5, A 2bcgskew Fused by a RHSP 2bcgskew RHSP
1st JILP Championship Branch Prediction (CBP-1) --- December 5, A 2bcgskew... 2bcgskew 4 component predictors: Bimodal Gshare (G0) Gshare (G1) Meta META selects between Majority vote BIM/G0/G1 BIM prediction [André Seznec, 2003]
1st JILP Championship Branch Prediction (CBP-1) --- December 5, A 2bcgskew... 2bcgskew Shared prediction tables: 2 N-1 bias G0/G1 2 N-2 bias BIM/META 2 N-2 hysteresis bits BIM/G0/G1/META Indexing: Bimodal pure addr G0 addr + 12 global hist G1 addr + 24 global hist META addr + 3 global hist
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Fusion principle Hybrid selects component based on META- predictor follows outcome of one component Fusion learns patterns from component outcomes improved accuracy if component outcomes differ [Gabriel Loh, 2002] Component predictors fusion Component predictors meta
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Fused by... Extracts multiple bits from 2bcgskew 9 outcome bits: 2bcgskew BIM bias + hysteresis G0 bias + hysteresis G1 bias + hysteresis META bias + hysteresis
1st JILP Championship Branch Prediction (CBP-1) --- December 5, a RHSP predictor RHSP [André Seznec, 2003]
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Information#bits Global History33 Local History6 Pseudo-tag8 Outcomes9 Bias1 Perceptron Predictor Local history table 512 entries indexed by branch address Pseudo-tag bits higher order address bits not used to select weights [André Seznec, 2003]
1st JILP Championship Branch Prediction (CBP-1) --- December 5, InformationRedundancy#bits Global Historypure33 1 Local Historypure Pseudo-tagpure Outcomespure9 Biaspure1 Redundant History Perceptron Predictor 116 n h5h4h3h2h1h0 n-th order redundancy of h: h5h4h3h2h1h0 x4x3x2x1x0
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Redundant History Skewed Perceptron Predictor InformationRedundancy#bitsBank 1Bank 2Bank 3Bank 4 Global Historypure Local Historypure Pseudo-tagpure Outcomespure99000 Biaspure
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Redundant History Skewed Perceptron Predictor Bank 1Bank 2Bank 3Bank 4 4 banks 32 entries = 5 bits index indexed by global history and rotation hashing function of branch address 8-bit weights MAC: (A+B, A-B) coding together 116 weights/entry a5a4 a0a1a2a3 r4r3r2r1r0 a8a7a6
1st JILP Championship Branch Prediction (CBP-1) --- December 5, Budget 2bcgskew 32K bits Fusion RHSP predictor 29K bits Local history 3K bits
Performance???
The end