A Specialized BTB Organization for Servers

Abstract

Contemporary server applications feature massive instruction footprints stemming from deeply layered software stacks. These footprints far exceed the capacity of the branch target buffer (BTB) and instruction cache (L1-I), resulting in the so-called front-end bottleneck. BTB misses may lead to wrong-path execution, triggering a pipeline flush when misspeculation is detected. Such pipeline flushes not only throw away tens of cycles of work but also expose the fill latency of the pipeline. Similarly, L1-I misses cause the core front-end to stall for tens of cycles while the miss is being served from lower-level caches.