Hacker News

points by throwaway17_17 4 days ago | 0 comments

My imagination is failing me, can you give me an example of the type of work being done where SIMD is ‘deeply probing and manipulating arbitrarily complex data structures in parallel that involve collections of unrelated types’? I don’t doubt you know what you mean, but I can’t wrap my head around it.

For me I can only think of the simplest example of SIMD being used to ‘parallelize loops’ as what SIMD is for. If it turns out I’m missing a large problem or application space for SIMD I will be excited to research it. Any pointers to topics would be appreciated.

[–] jandrewrogers 4 days ago

SIMD is often used to evaluate complex data structures in parallel. A common case is given a row with an arbitrary mix of data types and a query with an arbitrary mix of independent constraints on those data types, to evaluate all of the constraints in parallel in the same SIMD instruction(s).

The idea that SIMD is only good for parallelizing operations over arrays of the same type is empirically false and seriously understates the capabilities of good SIMD implementations. Some SQL-ish implementations work this way on row-structured data.

Most devs seriously underestimate what good SIMD is capable of.

[–] throwaway17_17 4 days ago

Thanks for the response, I’ll have some reading to do in this area.

[–] AlotOfReading 4 days ago

One example is OLAP databases, which often heavily exploit SIMD for query processing. You can also turn parsing into a SIMD problem, which is applicable to things like handling XML, JSON, and CSV. Simdjson comes to mind, or parabix for XML.

[–] throwaway17_17 4 days ago

The parsing stuff I am aware of, but the query processing is a big blank for me to dig into.

[–] bajard 3 days ago

I wrote an example answer, but it was shadowbanned