CppCon 2026

From our very first algorithms class, we are taught a simple rule: a better Big-O complexity means a faster algorithm. We spend years mastering asymptotic analysis, memorizing complexity tables, and losing sleep over worst-case scenarios. Big-O becomes a mental shortcut for “good” and “bad” code.

But the real world doesn’t run on whiteboards.

Modern performance is shaped far more by hardware realities than by asymptotic notation alone. CPUs have deep cache hierarchies, wide vector units, speculative execution, and memory systems that punish the “theoretically optimal” solution. GPUs thrive on massive parallelism where simple linear work can outperform asymptotically superior algorithms. Even on regular CPUs, cache-friendly linear scans often beat clever sub-linear approaches that fight memory latency.

In this talk, we will challenge the traditional Big-O mindset. We’ll look at classic algorithms through a modern lens and explore how hardware-aware designs cache-efficient layouts, SIMD/AVX vectorization, and parallel execution models can outperform algorithms with “worse” theoretical complexity. You’ll see why a higher Big-O algorithm can be faster, more scalable, and more predictable in practice.

The goal is not to dismiss Big-O, but to put it back in its proper place: as a tool, not a truth. By the end of this talk, you’ll think differently about performance and start writing code that works with the hardware, not against it.