Performance clearly matters to users. For example, the most common software update on the AppStore is “Bug fixes and performance enhancements.” Now that Moore’s Law has ended, programmers have to work hard to get high performance for their applications. But why is performance hard to deliver? I will first explain why current approaches to evaluating and optimizing performance don’t work. I’ll show how complicated performance has become on modern systems, and how compiler optimizations have essentially run out of steam. Next, I’ll introduce two radically new performance profilers that guide programmers directly to the code they need to change to improve application performance. The first is Coz, a new “causal profiler” for C/C++/Rust that lets programmers optimize for throughput or latency, and which pinpoints and accurately predicts the impact of optimizations via what we call “virtual speedup” experiments. Coz’s approach unlocks previously unknown optimization opportunities. Guided by Coz, we improved the performance…