Break dancing: low overhead, architecture neutral software branch tracing

Sampling-based Feedback Directed Optimization (FDO) methods like AutoFDO and BOLT that employ profiles collected in live production environments, are commonly used in datacenter applications to attain significant performance benefits without the toil of maintaining representative load tests. Sampled profiles rely on hardware facilities like Intel’s Last Branch Record (LBR) which are not currently available even on popular CPUs from ARM or AMD. Since not all architectures include a hardware LBR feature, we present an architecture neutral approach to collect LBR-like data. We use sampling and limited program tracing to capture LBR-like data from optimized and unmodified applications binaries. Since the implementation is in user space, we can collect arbitrarily long LBR buffers, and by varying the sampling rate, we can adjust the runtime overhead to arbitrarily low values. We target runtime overheads of