buzzword
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buzzword [2015/02/04 19:23] rachata |
buzzword [2015/02/06 19:21] albert lecture 10 words added |
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| ===== Lecture 9 (2/4 Wed.) ===== | ===== Lecture 9 (2/4 Wed.) ===== | ||
| - | | ||
| - | * Predicate combining (combine predicate for a branch instruction) | ||
| - | * Predicated execution (control dependence becomes data dependence) | ||
| * Definition of basic blocks | * Definition of basic blocks | ||
| * Control flow graph | * Control flow graph | ||
| Line 367: | Line 364: | ||
| * Two bits counter based prediction | * Two bits counter based prediction | ||
| * One more bit for hysteresis | * One more bit for hysteresis | ||
| + | |||
| + | ===== Lecture 10 (2/6 Fri.) ===== | ||
| + | * Branch prediction accuracy | ||
| + | * Why are they very important? | ||
| + | * Differences between 99% accuracy and 98% accuracy | ||
| + | * Cost of a misprediction when the pipeline is veryd eep | ||
| + | * Global branch correlation | ||
| + | * Some branches are correlated | ||
| + | * Local branch correlation | ||
| + | * Some branches can depend on the result of past branches | ||
| + | * Pattern history table | ||
| + | * Record global taken/not taken results. | ||
| + | * Cost vs. accuracy (What to record, do you record PC? Just taken/not taken info.?) | ||
| + | * One-level branch predictor | ||
| + | * What information are used | ||
| + | * Two-level branch prediction | ||
| + | * What entries do you keep in the global history? | ||
| + | * What entries do you keep in the local history? | ||
| + | * How many table? | ||
| + | * Cost when training a table | ||
| + | * What are the purposes of each table? | ||
| + | * Potential problems of a two-level history | ||
| + | * GShare predictor | ||
| + | * Global history predictor is hashed with the PC | ||
| + | * Store both GHP and PC in one combined information | ||
| + | * How do you use the information? Why does the XOR result still usable? | ||
| + | * Warmup cost of the branch predictor | ||
| + | * Hybrid solution? Fast warmup is used first, then switch to the slower one. | ||
| + | * Tournament predictor (Alpha 21264) | ||
| + | * Predicated execution - eliminate branches | ||
| + | * What are the tradeoffs | ||
| + | * What if the block is big (can lead to execution a lot of useless work) | ||
| + | * Allows easier code optimization | ||
| + | * From the compiler PoV, predicated execution combine multiple basic blocks into one bigger basic block | ||
| + | * Reduce control dependences | ||
| + | * Need ISA support | ||
| + | * Wish branches | ||
| + | * Compiler generate both predicated and non-predicated codes | ||
| + | * HW design which one to use | ||
| + | * Use branch prediction on an easy to predict code | ||
| + | * Use predicated execution on a hard to predict code | ||
| + | * Compiler can be more aggressive in optimimzing the code | ||
| + | * What are the tradeoffs (slide# 47) | ||
| + | * Multi-path execution | ||
| + | * Execute both paths | ||
| + | * Can lead to wasted work | ||
| + | * VLIW | ||
| + | * SuperScalar | ||
buzzword.txt · Last modified: 2015/04/27 18:20 by rachata
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