Optimizing existing large codebase How to measure The counters approach o use CPU counters to find out what happened during actual execution o do not slow down execution,so only do sampling The software instrumentation o run your code in a "virtual"environment o measure everything precisely o at the cost of speed perf tools bottlenecks 9/57 S.Ponce-CERNOptimizing existing large codebase 9 / 57 S. Ponce - CERN Measure Modernize Mem threads low level c/c perf tools bottlenecks How to measure The counters approach use CPU counters to find out what happened during actual execution do not slow down execution, so only do sampling The software instrumentation run your code in a “virtual” environment measure everything precisely at the cost of speed