Optimizing existing large codebase Measuire Modemiss Mem threads low Counters approach in practice o give precise timing of a realistic execution on your CPU ousing real cache prediction,actual vectorization,... using real CPU behavior(e.g.downclocking when overheating...) o allows to measure CPI (Cycles Per Instruction)and low level behavior in general (caching,pipelining) but data is only statistical so you need sufficient statistics o also not always reproducible,so hard to compare e.g.first test on cold processor,second on warm one Main tools available:perf and variants,Intel VTune ef tools bottlenecks 10/62 S.Ponce-CERNOptimizing existing large codebase 10 / 62 S. Ponce - CERN Measure Modernize Mem threads low level c/c perf tools bottlenecks Counters approach in practice give precise timing of a realistic execution on your CPU using real cache prediction, actual vectorization, ... using real CPU behavior (e.g. downclocking when overheating...) allows to measure CPI (Cycles Per Instruction) and low level behavior in general (caching, pipelining) but data is only statistical so you need sufficient statistics also not always reproducible, so hard to compare e.g. first test on cold processor, second on warm one Main tools available : perf and variants, Intel VTune