Speed issues megathread

[dalcde]

rust_ext

extend_maps_to_unit

This function is a huge bottleneck in the resolver when there are multiple products to compute. A good amount of time is used to compute products. This can be avoided if we enable the cache-multiplication feature, but this is only feasible for finite-dimensional algebras. One possible way to improve this is to use a fixed-size cache for infinite dimensional algebras to cache the multiplications that happen the most often.

Even if cache-multiplication is enabled, this function is still pretty slow. I haven't profiled this properly to figure out the bottleneck.

ext-websocket

compute_edges

The compute_edges function computes the structlines that we have to display on every page. Mathematically, what it does is that it expresses the matrix for the product in terms of the E_r page basis for each r. This function is the main bottleneck in ext-websocket.

It is not entirely clear to me why this function is so slow. One possibility is just that there are many products to compute. Another possibility is that grouping the products by product type instead of the bidegree makes it slow if we want to compute the products with a fixed bidegree.

[dalcde]

One possible thing that might help is to define versions of fp_vector functions where we know that the vectors are not sliced to save some checks.

[hoodmane]

Also, using unsafe functions to access elements of arrays without checking array bounds in the performance critical functions and in general skip whatever automatic checking Rust does would probably be a good idea. If we do this, we might also add more unit tests to reduce the probability of weird edge case errors.