[WorldMaker]

The performance improvements between .NET Core (any version) and (just) .NET 5+ have been pretty astounding. I've seen some incredible micro-benchmarks where the same code running in .NET 5+ hugely outperforms anything running in a version <= 4 (both .NET Core and the old .NET Framework). Factor in what you can do in memory-bound code by rewriting it to use .NET 5+ things like Span<T> and stackalloc there's no question that at this point you should be able to get much better performance out of .NET 5+. If performance was your bottleneck in .NET Core, the latest .NET versions (6 [LTS] or 7 [Preview]) may be worth checking out.

GUI stuff is also what happened in .NET 5+. WinForms and WPF were both added to .NET 5. There's some porting that needs to happen and not all old WinForms/WPF code will be happy on .NET 5+. The biggest remaining "missing piece" from a GUI perspective is that a lot of old WinForms/WPF code used WCF for service code. I think porting WCF to use simpler REST services is easy enough and there's lots of people doing that with gRPC services in .NET 5+ too. There's also the Open Source CoreWCF project that is trying to hit compatibility with the most used bindings in WCF on top of .NET 5+.

[dundarious]

The relevant part were our model calculations and it was already heavily optimized (no allocations, etc.), so none of the new library stuff would help at all. We just found that Linux .NET Core underperformed compared to Windows .NET anything (Framework or Core). Maybe our methodology was wrong, but we had a few people look at it, made the comparison in several ways, and generally tried to be quite thorough. We always found Linux (only .NET Core) had ~0.9x the performance of Windows (any .NET) — and we were a mostly Linux shop, running C/C++ apps, so our Linux build was appropriately tuned. Given .NET Core was relatively new at the time, and Framework still had some legs, we didn’t dig down as far as looking at IR or JIT output, because we could afford to wait. After all, one of the draws was to reduce problems due to using our fancy network cards+stack in Windows, so there was no point in adding complexity from a new Linux .NET runtime, including complexity from having to troubleshoot performance.

I’ve been saying “we”, but I left that job a couple years ago so I won’t be trying any new .NET versions myself :-)