[xtalax-droid]

Problem

The PrecompileTools workload in src/precompile.jl has been disabled (if false) since the compat update, so every fresh Julia process paid roughly 40-60 s of compilation on the first discretize call, plus 8-13 s for mtkcompile and 5-27 s for ODEProblem. Warm calls take milliseconds, so this is almost entirely inference and codegen. A SnoopCompile profile showed the time spread over hundreds of Base, SymbolicUtils and ModelingToolkit specializations rather than any single MOL hot spot, so re-enabling the workload was preferred over targeted edits.

Fix

The workload is rewritten and re-enabled. It runs discretize, symbolic_discretize, mtkcompile and ODEProblem on:

• 1D diffusion with a Dirichlet left and Neumann right boundary.
• 1D advection-diffusion, periodic, with UpwindScheme and WENOScheme.
• A 2D two-variable periodic reaction-diffusion system.

Periodic systems use should_transform = false so precompilation stays quiet (periodic boundaries are interfaces, so the transformation is skipped for them regardless). No new dependencies; PrecompileTools was already in [deps] and [compat].

Results

Cold = first call in a fresh process. Median of 3 fresh processes, Julia 1.12.1, 32-core box with some load from other jobs.

system	discretize	mtkcompile	ODEProblem	first solve
heat1d_dirichlet_neumann	41.4 -> 0.64 s	8.1 -> 0.06 s	5.3 -> 0.51 s	5.1 -> 5.1 s
weno_advection1d	51.7 -> 0.88 s	10.6 -> 0.29 s	6.6 -> 2.04 s	13.7 -> 11.6 s
brusselator2d N=32	61.1 -> 4.71 s	12.6 -> 2.3 s	27.1 -> 18.4 s	14.2 -> 11.7 s

Cost: package precompile goes from about 9 s to about 87 s wall, and the MethodOfLines cache from 4.5 MB to 139 MB. If that is too much, the 2D case is the first thing to drop (about 4 s of brusselator discretize).

What remains is compile time of the generated RHS (ODEProblem and first solve). That lives in ModelingToolkit, RuntimeGeneratedFunctions and OrdinaryDiffEq and is not addressed here.

Tests

GROUP=Components and GROUP=QA (21/21) pass on the final commit; Runic is clean.

Review notes

• The workload runs at precompile time, so an API change that makes a workload system throw breaks using MethodOfLines, not just a test.
• Coverage is the systems above; staggered grids, pseudospectral, 3D and higher orders still compile cold.

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🤖 Posted by an AI agent · harness: Claude Code 2.1.309 · model: claude-sonnet-5-5
Review: unreviewed
Session: 47ff55ef-8952-4078-8e4e-77c72c85d6c4