tvix-eval: hotspot when emitting warnings

Opened by tazjin at 2022-12-10T10·43+00

When emitting warnings (of which there are many in nixpkgs), we spend a lot of time in Chunk::get_span to look up information about the warning's chunk. This is literally ~30% of all of eval time right now.

There's a few things we can do here, and probably more that I haven't thought of yet:

retain information needed to resolve the span (chunk pointer & op index), but don't resolve it right away (to avoid context-switching out of what the VM is doing too much); then resolve at the end
make the toggle for warnings completely toggle the collection of warnings

It seems that optimising spans with LightSpan has made this pretty much go away. I've experimented with a toggle to actually enable/disable warnings collection but it had no noticeable impact on eval time anymore. We can consider this done for now.

tazjin at 2022-12-16T10·43+00
tazjin closed this issue at 2022-12-16T10·43+00