SciML/OrdinaryDiffEq.jl

Refactor some core functionality into smaller functions for more compilation cache reuse

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#229 opened on Nov 27, 2017

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Description

As noted in this post (https://stackoverflow.com/questions/47501844/julia-differentialequations-jl-speed/47507933#47507933), DiffEq aggressively specializes on each function. This causes a compilation phase between each new ODE function. However, we can lessen that burden by making less functions (or parts of functions) explicitly depend on the ODE function. Since the integrator is strongly typed with the function, this would mean writing some functions as independent of the integrator. For example, this used to be inline in the init function:

https://github.com/JuliaDiffEq/OrdinaryDiffEq.jl/blob/master/src/solve.jl#L329-L362

but since it's now refactored out, it's compiled one and shared between all functions. I am not sure how to profile compilation time, but I would believe most of the time is spent in the "inner logic" functions here:

https://github.com/JuliaDiffEq/OrdinaryDiffEq.jl/blob/master/src/integrators/integrator_utils.jl

All of these functions are functions of integrator which is why they specialize each time, but many of them are not dependent on f so it may be possible to make this not specialize on f.

Contributor guide

Tech stack
None
Domain
backendperformance
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Julia programmingtype specializationOrdinaryDiffEq.jl internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the functions in src/integrators/integrator utils.jl that depend on the integrator type but not on the ODE function f. Read the blog post referenced for background on compilation specialization. Profile compilation time using Julia's built in tools to identify bottlenecks. Look at the refactoring example in solve.jl (lines 329-362) which was made independent of the integrator. Propose making similar changes to independent functions to reduce recompilation.