PeriPragmaton

Notes on performance: the places where the hardware, the compiler or the runtime stops behaving like the model most of us carry in our heads, and what that costs. Each post comes with the code and the benchmark that produced its numbers, in darfire/bloggy-code.

Recent

Playing with Profile-Guided Optimization

October 25, 2026·13 mins

Compilers Performance

What the compiler has to guess about your program, and what changes when it doesn’t have to. Profile-guided optimization on a toy interpreter and on SQLite.

Under Pressure: Mind the Instruction Cache

October 17, 2026·7 mins

CPU Caches Performance

What happens when a hot loop runs through more code than the instruction cache can hold, and why batching work is a design decision the compiler won’t make for you.

Quirks of a CPU: Cache Aliasing

October 11, 2026·11 mins

CPU Caches Performance

Summing a power-of-two-sized matrix column by column is eight times slower than the same loop with one extra element per row. Why cache sets make some addresses collide, and how to spot it.