On: I/O library 6x faster than fmt, 10x faster than stdio.h and iostream

> All i/o libraries eventually hit OS barrier

Indeed.

> I can't really see how it could be optimised to gain 6x speed up.

Performance claims appear to not even be based on I/O but only on two formatting microbenchmarks and are severely misleading https://news.ycombinator.com/item?id=23311726