Kernel team completes the scheduler rewrite

August 19, 2026 by Mila Cache

Three years and one abandoned prototype later, the fair-share scheduler that has run ferdiOS since its first release has been retired in favour of a design built around latency guarantees rather than throughput.

The patch series merged quietly on Tuesday evening, without an announcement, which is roughly how the kernel team has handled every milestone in this project. It is nevertheless the largest single change to the ferdiOS kernel in a decade.

Why replace something that worked

The old scheduler was fair, and fairness was the problem. It divided processor time evenly among everything that asked for it, which is the correct behaviour for a build server and a slightly wrong one for a laptop running a browser, a compiler and an audio stack at the same time.

The replacement does not attempt to be fair. It asks each task what latency it can tolerate and then tries not to violate that number.

Build throughput is, within measurement error, unchanged. That was the constraint the team set themselves at the start: no regression on the workload the distribution is actually known for.

The abandoned prototype

The first attempt, started in 2023, tried to infer latency requirements from a task’s behaviour rather than have it declare them. It worked well in benchmarks and badly everywhere else.

Anything that guesses will eventually guess wrong on the one workload you care about. We spent a year learning that.

The current design requires an explicit declaration, with a conservative default for everything that says nothing. Most programs will never need to touch it.

What users will notice

Very little, which is the intent. Desktop sessions should feel steadier under load, and audio work that previously needed a specially tuned kernel should now be possible on the stock one. Anyone running ferdiOS purely as a build machine can carry on as before.