An analysis of dynamic branch prediction schemes on system workloads
Nicolas Gloy, Cliff Young, J. Bradley Chen, Michael D. Smith · 1996
Recent studies of dynamic branch prediction schemes rely almost exclusively on user-only simulations to evaluate performance. We find that an evaluation of these schemes with user and kernel refer-ences often leads to different conclusions. By analyzing our own Atom-generated system traces and the system traces from the Instruction Benchmark Suite, we quantify the effects of kernel and user interactions on branch prediction accuracy. We find that user-only traces yield accurate prediction results only when the kernel accounts for less than 5~o of the total executed instructions. Schemes that appear to predict well under user-only traces are not always the most effective on full-system traces: the recently-pro-posed two-level adaptive schemes can suffer from higher aliasing than the original per-branch 2-bit counter scheme. We also find that flushing the branch history state at fixed intervals does not accu-rately model the true effects of user/kernel interaction.