# Time to build system and problem is slower in Julia 1.12 with MTKv11

**URL:** <https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536>\
**Category:** Performance\
**Tags:** modelingtoolkit, ttfx\
**Created:** [February 9, 2026, 8:36am UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536 "2026-02-09T08:36:53Z")\
**Posts on this page:** 13\
**Page:** 1

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**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [February 9, 2026, 8:36am UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/1 "2026-02-09T08:36:53Z")

</div>

Hi, while I was trying the new version (v11) of ModelingToolkit.jl , I noticed it took longer to build the ODE system and problem under Julia 1.12.

Here is the GitHub actions [workflow](https://github.com/sosiristseng/mtk-ttfx/actions/runs/21794373776) running the script

```julia
using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
using OrdinaryDiffEq

@parameters τ = 3.0 # parameters
@variables x(t) = 0.0 # dependent variables
eqs = [D(x) ~ (1 - x) / τ]

@time "Build system" @mtkcompile fol = System(eqs, t)
@time "Build problem" prob = ODEProblem(fol, [], (0.0, 10.0))
@time "Solve problem" sol = solve(prob, Tsit5())

```

Time for building the `ODESystem` / `ODEProblem` in seconds.

| MTK | JL1.10 | JL1.12 |
| --- | --- | --- |
| v10 | 1.25/2.04 | 0.76/1.89 |
| v11 | 1.91/1.35 | 33.44/17.37 |

Is there anything I can do to reduce the first time to build systems/problems in 1.12?

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<div class="post-metadata">

**Author:** ![cryptic.ax](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cryptic.ax/32/220540_2.png) [@cryptic.ax](https://discourse.julialang.org/u/cryptic.ax)\
**Post date:** [February 9, 2026, 10:09am UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/2 "2026-02-09T10:09:35Z")

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Hi! Thanks for reporting this. This is certainly very abnormal, and I’ve gone to great lengths to ensure that TTFX of MTKv11 on 1.12 is as fast as possible. I’ll investigate what’s going on here. Before I do, I’ll need a little more information.

- What versions of ModelingToolkit, ModelingToolkitBase, ModelingToolkitTearing, Symbolics and SymbolicUtils are you running?
- Did you run the above code in the REPL or as a script?
- What packages do you have in your global environment on each Julia version?
- Did you use the `--project` flag when starting Julia? If you didn’t, and if you ran the code in a script file, how did you load the appropriate environment?

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<div class="post-metadata">

**Author:** ![baggepinnen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baggepinnen/32/693_2.png) [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)\
**Post date:** [February 9, 2026, 10:16am UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/3 "2026-02-09T10:16:32Z")

</div>

All questions should be answered in the linked CI workflow? [fix · sosiristseng/mtk-ttfx@68045eb · GitHub](https://github.com/sosiristseng/mtk-ttfx/actions/runs/21794373776)

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<div class="post-metadata">

**Author:** ![cryptic.ax](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cryptic.ax/32/220540_2.png) [@cryptic.ax](https://discourse.julialang.org/u/cryptic.ax)\
**Post date:** [February 9, 2026, 10:17am UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/4 "2026-02-09T10:17:06Z")

</div>

Ah, thanks. Somehow I glossed over that part.

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<div class="post-metadata">

**Author:** ![cryptic.ax](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cryptic.ax/32/220540_2.png) [@cryptic.ax](https://discourse.julialang.org/u/cryptic.ax)\
**Post date:** [February 9, 2026, 12:41pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/5 "2026-02-09T12:41:53Z")

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A quick mockup of your example indeed reproduces compile time differences, but not nearly as significant as in your CI. I get

Julia 1.10:

```julia-auto
Build system: 0.662157 seconds (1.43 M allocations: 106.126 MiB, 1.52% gc time, 99.15% compilation time)
Build problem: 0.568265 seconds (1.26 M allocations: 90.375 MiB, 1.43% gc time, 94.27% compilation time)

```

Julia 1.12:

```julia-auto
Build system: 2.221802 seconds (2.72 M allocations: 139.684 MiB, 1.89% gc time, 99.62% compilation time: 100% of which was recompilation)
Build problem: 3.862440 seconds (25.89 M allocations: 1.300 GiB, 2.59% gc time, 99.53% compilation time: 62% of which was recompilation)

```

All of the time is Julia compile time. I’m not yet sure why it increased so dramatically.

---

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [February 9, 2026, 12:42pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/6 "2026-02-09T12:42:39Z")

</div>

Thanks for the reply.

1. I need to print manifest in the CI.
2. I ran it as a script: `julia test.jl`
3. There is no global packages installed (prior to point 4). The CI spins a fresh environment every time.
4. By point 3, I just install all packages in the global environment.

Edit: Added pkg versions

```julia-auto
  [961ee093] ModelingToolkit v11.9.0
  [7771a370] ModelingToolkitBase v1.12.0
  [6bb917b9] ModelingToolkitTearing v1.2.6
  [d1185830] SymbolicUtils v4.17.0
  [0c5d862f] Symbolics v7.13.0

```

Output of `versioninfo()`:

```julia-auto
Julia Version 1.10.10
Commit 95f30e51f41 (2025-06-27 09:51 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × AMD EPYC 7763 64-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, znver3)
Threads: 4 default, 0 interactive, 2 GC (on 4 virtual cores)
Environment:
  JULIA_CI = true
  JULIA_NUM_THREADS = auto

```

```julia-auto
Julia Version 1.12.4
Commit 01a2eadb047 (2026-01-06 16:56 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 4 × AMD EPYC 7763 64-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, znver3)
  GC: Built with stock GC
Threads: 4 default, 1 interactive, 4 GC (on 4 virtual cores)
Environment:
  JULIA_CI = true
  JULIA_NUM_THREADS = auto

```

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<div class="post-metadata">

**Author:** ![cryptic.ax](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cryptic.ax/32/220540_2.png) [@cryptic.ax](https://discourse.julialang.org/u/cryptic.ax)\
**Post date:** [February 9, 2026, 1:10pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/7 "2026-02-09T13:10:18Z")

</div>

It seems something invalidated the `mtkcompile` method recently, so it doesn’t precompile.

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<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [February 28, 2026, 12:44pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/8 "2026-02-28T12:44:08Z")

</div>

It seems like TTFX in Julia 1.12 is much faster after [MTK v11.13](https://github.com/SciML/ModelingToolkit.jl/releases/tag/v11.13.0), demonstrated by [this GitHub CI run](https://github.com/sosiristseng/mtk-ttfx/actions/runs/22510259974).

Thank you SciML team!

---

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [April 16, 2026, 1:42pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/9 "2026-04-16T13:42:16Z")

</div>

Here’s an update. I wonder if package loading affects invalidations.

I found that adding a line `using Plots` might increase time to build first modeling significantly.

```julia
using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
using OrdinaryDiffEq

## HH neuron model for example
function hh_sys(; name=:hh)
    exprel(x) = x / expm1(x)
    @discretes iStim(t)=0.0
    @parameters E_N=55 E_K=-72 E_LEAK=-49 G_N_BAR=120 G_K_BAR=36 G_LEAK=0.3 C_M=1
    @variables v(t)=-59.8977 m(t)=0.0536 h(t)=0.5925 n(t)=0.3192 iNa(t) iK(t) iLeak(t) ma(t) mb(t) ha(t) hb(t) na(t) nb(t)

    ## Electrical stimulation events
    stim_on_1 = ModelingToolkit.SymbolicDiscreteCallback([20.0] => [iStim ~ -6.6], discrete_parameters = iStim, iv = t)
    stim_off_1 = ModelingToolkit.SymbolicDiscreteCallback([21.0] => [iStim ~ 0.0], discrete_parameters = iStim, iv = t)
    stim_on_2 = ModelingToolkit.SymbolicDiscreteCallback([60.0] => [iStim ~ -6.9], discrete_parameters = iStim, iv = t)
    stim_off_2 = ModelingToolkit.SymbolicDiscreteCallback([61.0] => [iStim ~ 0.0], discrete_parameters = iStim, iv = t)

    eqs = [
        ma ~ exprel(-0.10 * (v + 35)),
        mb ~ 4.0 * exp(-(v + 60) / 18.0),
        ha ~ 0.07 * exp(-(v + 60) / 20),
        hb ~ 1 / (exp(-(v + 30) / 10) + 1),
        na ~ 0.1 * exprel(-0.1 * (v + 50)),
        nb ~ 0.125 * exp(-(v + 60) / 80),
        iNa ~ G_N_BAR * (v - E_N) * (m^3) * h,
        iK ~ G_K_BAR * (v - E_K) * (n^4),
        iLeak ~ G_LEAK * (v - E_LEAK),
        D(v) ~ -(iNa + iK + iLeak + iStim) / C_M,
        D(m) ~ -(ma + mb) * m + ma,
        D(h) ~ -(ha + hb) * h + ha,
        D(n) ~ -(na + nb) * n + na
    ]
    sys = System(eqs, t; name, discrete_events=[stim_on_1, stim_off_1, stim_on_2, stim_off_2])
    return sys
end

## Fast, took less than 10 seconds
tend = 100.0
@time "Build system" @mtkcompile sys = hh_sys()
@time "Build problem" prob = ODEProblem(sys, [], tend)
@time "Solve problem" sol = solve(prob, TRBDF2())

```

But if I also load Plots.jl alongside MTK, it took much longer to build packages.

```julia
using ModelingToolkit
using ModelingToolkit: t_nounits as t, D_nounits as D
using OrdinaryDiffEq
using Plots ## <------ This line
Plots.default(size=(800, 600))
#====
The same HH neuron model above
====#

## Slow, took a minute on my computer
tend = 100.0
@time "Build system" @mtkcompile sys = hh_sys()
@time "Build problem" prob = ODEProblem(sys, [], tend)
@time "Solve problem" sol = solve(prob, TRBDF2())

```

I am reproducing this on GitHub actions: [add info · sosiristseng/mtk-ttfx@984825a · GitHub](https://github.com/sosiristseng/mtk-ttfx/actions/runs/24514004739/job/71652680508)

I would like to work around (or even better, resolve) this issue. What could I do?

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [April 16, 2026, 2:34pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/10 "2026-04-16T14:34:06Z")

</div>

We will retime after the OrdinaryDiffEq.jl v7 which greatly reduces invalidations

---

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [April 16, 2026, 2:39pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/11 "2026-04-16T14:39:03Z")

</div>

Thank you for your prompt reply, @ChrisRackauckas. Currently I could work around it through a startup package with `PrecompileTools.@recompile_invalidations`: [Home · PrecompileTools.jl](https://julialang.github.io/PrecompileTools.jl/stable/#Tutorial:-%22healing%22-invalidations).

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [April 16, 2026, 2:39pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/12 "2026-04-16T14:39:36Z")

</div>

Yes, precompilation after invalidations, i.e. in your environment, does solve it.

---

<div class="post-metadata">

**Author:** ![Wen-Wei\_Tseng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wen-wei_tseng/32/28839_2.png) [@Wen-Wei\_Tseng](https://discourse.julialang.org/u/Wen-Wei_Tseng)\
**Post date:** [April 17, 2026, 3:23pm UTC](https://discourse.julialang.org/t/time-to-build-system-and-problem-is-slower-in-julia-1-12-with-mtkv11/135536/13 "2026-04-17T15:23:38Z")

</div>

In case someone want to know how to do this: [mtk-ttfx/Startup/src/Startup.jl at main · sosiristseng/mtk-ttfx · GitHub](https://github.com/sosiristseng/mtk-ttfx/blob/main/Startup/src/Startup.jl)

I also tried `@recompile_invalidations` but sometimes it generated a warning `AssertionError(msg="irinterp is unable to handle heavy recursion correctly")`.