> The background on our side is that we did do quite a lot of profiling and investigation of the current evaluator - last year, informally, over video chats and IRC. We have a bunch of logs and various perf measurements spread out over some machines but right now the knowledge lives in our heads, mostly because at the time we did not expect this to spawn a serious project.
It's good to hear that you did do some profiling, even if the results are not public! Of course I would not expect the details in the initial announcement, but I would have expected a mention of this work. At least I have a much higher confidence in the success of this project now than just after reading the announcement.
Switching between the proper implementation of high-level concepts is a staple of untyped (and sometimes typed) runtimes, so in this context the changeset makes more sense than simply "replacing an array-backed implementation with an std::vector-backed implementation" as described, thanks for the explanation!
I'm also not putting any blame on Nix --- the fact that the performance of the evaluator is such an issue is in a way a testament to its success. Unfortunately large, long-lived systems do require active care to enforce proper boundaries between subsystems, and it's a shame if it has got to a point where it's no longer possible to reinstate that separation.
It's good to hear that you did do some profiling, even if the results are not public! Of course I would not expect the details in the initial announcement, but I would have expected a mention of this work. At least I have a much higher confidence in the success of this project now than just after reading the announcement.
Switching between the proper implementation of high-level concepts is a staple of untyped (and sometimes typed) runtimes, so in this context the changeset makes more sense than simply "replacing an array-backed implementation with an std::vector-backed implementation" as described, thanks for the explanation!
I'm also not putting any blame on Nix --- the fact that the performance of the evaluator is such an issue is in a way a testament to its success. Unfortunately large, long-lived systems do require active care to enforce proper boundaries between subsystems, and it's a shame if it has got to a point where it's no longer possible to reinstate that separation.