Characterizing the Mispredicted Branches

Studies of branch prediction have tended to emphasize aggregate measurement of prediction performance. Instead, we have taken the approach that there are likely to be a small number of branch addresses ("sites") in the program causing the majority of all mispredictions. Using a graphical tool we developed for analyzing program traces on-the-fly, we present three interesting results, all based on measurement of benchmarks including a subset of the SPEC92 suite of programs: ffl More than 90% of all misses can be attributed to the top 0.5% of sites causing branch mispredictions. Additionally, the top fifty sites account for more than 86% all mispredictions. ffl For these popular misprediction sites, the distance in dynamic instructions until the next mispredicted site is quite large on average (more than 50-200 instructions), making exotic techniques such as guarded execution seem feasible. ffl Finally, we found that these sites exhibited larger than average miss rates, indicating that..