> Unfortunately on Linux it seems like there is a large performance tradeoff

Implementing transitive priority inheritance is just inherently algorithmically more expensive: there's no avoiding that.

> Sometimes I feel like trying to use Linux for realtime is an effort in futility.

If you're not actually using an RT kernel, yeah, it's futile. But if you are, the guarantees are pretty strong... on x86 PCs, the hardware gets in the way much more than the software in my experience. There's a lot of active work upstream.

The Linux priority inheritance futexes are also fair, which adds unnecessary overhead if you only care about PI, not fairness.