Tuning Julia code

Preparation

• Install Julia (ideally 1.10 or newer)
• Install OSCAR
• Install more Julia packages:

  ]add Revise BenchmarkTools SnoopCompile SnoopCompileCore JET Cthulhu PProf ProfileView AllocCheck DispatchDoctor
  

• I heartily recommend https://modernjuliaworkflows.org/
• In fact let’s start out tour from there!

Allocations

• Some of our tests take particular long or use a lot of memory
• Memory consumption is often a good proxy for performance
  • many temporary allocations -> lots of cleanup -> wasted effort
• GOAL: reduce allocations
• Example: creating a polynomial ring

julia> n=2; R=QQ; @btime S, _ = polynomial_ring(R, "y" => 1:n, "t" => 1:n);
  3.271 μs (83 allocations: 3.50 KiB)

julia> n=2; R=QQ; @btime S, _ = polynomial_ring(R, :y => 1:n, :t => 1:n);
  2.319 μs (51 allocations: 2.27 KiB)

• Be careful about using gens repeatedly

julia> S, (y,t) = polynomial_ring(R, :y => 1:n, :t => 1:n);

julia> @btime gens(S)[1:n];
  431.950 ns (15 allocations: 688 bytes)

julia> @btime y;
  1.500 ns (0 allocations: 0 bytes)

• there is a reason ngens exists

julia> @btime length(gens(S));
  407.797 ns (13 allocations: 592 bytes)

julia> @btime ngens(S);
  46.638 ns (0 allocations: 0 bytes)

• some rings allow gens(S; copy=false)

Some OSCAR case studies

@ experimental/FTheoryTools/test/literature_models.jl:1 @
# runs 400 seconds, allocates 80 GB

@ experimental/FTheoryTools/test/tate_models.jl:1 @
# runs 215 seconds, allocates 65 GB

@ test/AlgebraicGeometry/Schemes/elliptic_surface.jl:1 @
# runs 480 seconds, allocates 122 GB

• literature_models.jl has 800 lines, where are the memory hogs?
  • look at recent CI logs to get an idea
  • e.g. this log then search for e.g. “defining data for literature” (name of a @testset)
  • leads us to Test weierstrass form of models in F-theory on all toric hypersurfaces, defined over concrete base

Some Relevant packages

Measuring

• https://github.com/JuliaCI/BenchmarkTools.jl
• https://github.com/LilithHafner/Chairmarks.jl

Profiling

• built-in profiling code (Docs)
• https://github.com/JuliaPerf/PProf.jl
• ProfileView
• ProfileCanvas
• ProfileSVG

Type stability

• https://github.com/aviatesk/JET.jl (Docs)
• https://github.com/JuliaDebug/Cthulhu.jl

Other

• https://github.com/JuliaLang/AllocCheck.jl (Docs)
• https://github.com/timholy/SnoopCompile.jl (Docs, the docs contain multiple nice tutorials)
• https://github.com/MilesCranmer/DispatchDoctor.jl