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<html>
<head>
<title>Improvements in package precompilation</title>
<link rel="stylesheet" href="node_modules/reveal.js/dist/reveal.css">
<link rel="stylesheet" href="node_modules/reveal.js/dist/theme/white.css">
<link rel="stylesheet" href="mystyles.css">
</head>
<body>
<div class="reveal">
<div class="slides">
<section>
<h2>Improvements in package precompilation</h2>
<br>
<p style="text-align:center;font-size:40px;line-height:20px">Timothy E. Holy</p>
<p style="text-align:center;font-size:20px">Washington University in St. Louis</p>
<br>
<p style="text-align:center;font-size:40px;line-height:20px">Valentin Churavy</p>
<p style="text-align:center;font-size:20px">Massachusetts Institute of Technology</p>
</section>
<section data-markdown>
<script type="text/template">
### Julia runs fast
---
### You can write fast code quickly
- <!-- .element: class="fragment" data-fragment-index="1" --> Python `dask.array`: ~12,000 lines of code
- <!-- .element: class="fragment" data-fragment-index="2" --> Julia: 18 lines of code
---
### But Julia has a major usability problem: latency, aka Time To First eXecution (TTFX)
Julia:
```julia
using GLMakie
plot(rand(10))
```
Python: <!-- .element: class="fragment" data-fragment-index="1" -->
```python
import matplotlib.pyplot as plt
from numpy import random
plt.plot(random.rand(10))
plt.show()
```
<!-- .element: class="fragment" data-fragment-index="1" -->
---
### The two halves of TTFX
- package loading (a subject for a later day)
- code compilation (our current target)
---
### Strategies to reduce compilation time
- make the compiler faster
- compile as little as needed (LLVM compile-on-demand) <!-- .element: class="fragment" data-fragment-index="1" -->
- re-use the compiled code: better precompilation <!-- .element: class="fragment" data-fragment-index="2" -->
---
### Why precompilation is important
</script>
</section>
<section data-markdown
data-transition="slide-in fade-out">
<script>
### What gets saved from Julia's compilation pipeline?
</script>
</section>
<section data-markdown
data-transition="fade-in fade-out">
<script>
### What gets saved from Julia's compilation pipeline?
</script>
</section>
<section data-markdown
data-transition="fade-in fade-out">
<script>
### What gets saved from Julia's compilation pipeline?
</script>
</section>
<section data-markdown
data-transition="fade-in slide-out">
<script>
### What gets saved from Julia's compilation pipeline (Julia 1.0-1.7)?
</script>
</section>
<section data-markdown>
<script type="text/template">
### Challenges to more comprehensive precompilation: invalidation
Julia has to discard compiled code if it's no longer valid. How does this happen?
```julia
f(::Integer) = 1
g(x) = f(x)
g(1) # compiles g(::Int) and f(::Int)
```
But now define <!-- .element: class="fragment" data-fragment-index="1" -->
```julia
f(::Int) = 2
```
<!-- .element: class="fragment" data-fragment-index="1" -->
and the compiled code for <!-- .element: class="fragment" data-fragment-index="2" --> `g(::Int)` <!-- .element: class="fragment" data-fragment-index="2" --> has to be discarded (`f(::Int) from f(::Integer)` is no longer used).
---
### How common is invalidation?
<span style="font-weight:700;font-size:20px">
Fewer invalidations => more benefit from precompilation
</span>
---
### What gets saved from Julia's compilation pipeline (Julia 1.8)?
</script>
</section>
<section data-markdown
data-transition="slide-in fade-out">
<script>
### Some benchmarks
</script>
</section>
<section data-markdown
data-transition="fade-in fade-out">
<script>
### Some benchmarks
</script>
</section>
<section data-markdown
data-transition="fade-in slide-out">
<script>
### Some benchmarks
</script>
</section>
<section data-markdown>
<script type="text/template">
### Custom precompilation: `Startup.jl`
`~/.julia/config/startup.jl`:
```julia
using Startup
```
`~/.julia/dev/Startup/src/Startup.jl`: <!-- .element: class="fragment" data-fragment-index="1" -->
```julia
module Startup
import Pkg1, Pkg2, Pkg3
# force precompilation of `somefunction` and its dependents
Pkg1.somefunction(rand(10))
⋮
end
```
<!-- .element: class="fragment" data-fragment-index="1" -->
New package: <!-- .element: class="fragment" data-fragment-index="2" --> `SnoopPrecompile.jl` <!-- .element: class="fragment" data-fragment-index="2" -->
---
### Comparing Startup.jl vs PackageCompiler
| | Startup.jl | PackageCompiler |
|:---------:|:------------:|:-----------------:|
| Load time | **Poor** | **Good** |
| Inferred code saved | Yes | Yes |
| Native code saved | **No** | **Yes** |
| Works with Pkg updates | **Yes** | **No** |
<!-- .element.table: style="font-size:100%;" -->
---
### Looking ahead: saving native code in package precompilation
Julia has two independent systems for storing code in files:
| | `dump.c` | `staticdata.c` |
|:----- |:--------:|:--------------:|
| Lowered code | Yes | Yes |
| Type-inferred code | Yes | Yes |
| Native code | **No** | **Yes** |
| Usable for packages | **Yes** | **No** |
<!-- .element.table: style="font-size:100%;" -->
</script>
</section>
<section data-markdown
data-transition="slide-in fade-out">
<script>
### What's needed to support packages in `staticdata.c`?
Work has started: see PR#44527
</script>
</section>
<section data-markdown
data-transition="fade-in fade-out">
<script>
### What's needed to support packages in `staticdata.c`?
Work has started: see PR#44527
</script>
</section>
<section data-markdown
data-transition="fade-in fade-out">
<script>
### What's needed to support packages in `staticdata.c`?
Work has started: see PR#44527
</script>
</section>
<section data-markdown
data-transition="fade-in slide-out">
<script>
### What's needed to support packages in `staticdata.c`?
Work has started: see PR#44527
</script>
</section>
<section data-markdown>
<script type="text/template">
### Challenges
- De-duplication: `PkgA.f(::Integer)` gets specialized as `f(::Int)` in *both* `PkgB` and `PkgC`, these two (identical) specializations must be merged.
- Invalidation: must check validity of compiled code upon loading <!-- .element: class="fragment" data-fragment-index="1" -->
All this exists in <!-- .element: class="fragment" data-fragment-index="2" --> `dump.c`. <!-- .element: class="fragment" data-fragment-index="2" -->
---
### A common challenge
Compiling Julia to native code is "easy", as long as you...
- **Don't** use the Julia runtime (GC, exceptions, multi-threading, IO, ...)
- **Don't** use global data
- **Don't** have dynamic dispatch
---
### GPUCompiler.jl
GPUCompiler.jl provides infrastructure to exfiltrate "near static" code.
- CUDA.jl/AMDGPU.jl/... very limited runtime on device
- Enzyme.jl: Compiling code within the same instance of Julia through a parallel JIT
- StaticCompiler.jl: Originally limited runtime environment, now linking against libjulia.
---
### From `sysimage` to `pkgimage`
Each `.ji` becomes a `.so`:
1. Contains the metadata information for inserting methods into the method-table
2. Precompiled code cache
3. *New:* Object code cache
Object code cache must be *relocatable*.
---
### Relocating code
1. Global data is owned/rooted by the module in which it was declared
2. Will be serialized into the corresponding `pkgimage`.
3. Dependent compilation replaces references to these objects with relocation entries
4. Relocation will be performed by the `pkgimage` loader in Julia.
Implemented in PR#44527, **but** functions are unecessarily duplicated.
---
### Relocation is implementing save & load for the arrows
---
### Next steps
1. During codegen detect that call target has already been compiled, and replace with relocation/trampoline.
2. Automate the process and integrate into precompilation
3. Enable package loading to `pkgimage`s
4. (Speculative) Can we support `@ccallable`?
---
### A hopeful future
Julia 1.8: less invalidation, more comprehensive precompilation than any prior Julia version
On the horizon: comprehensive precompilation of native code <!-- .element: class="fragment" data-fragment-index="1" -->
Not yet started: <!-- .element: class="fragment" data-fragment-index="2" -->
- improvements in load times <!-- .element: class="fragment" data-fragment-index="2" -->
- tools for streamlining the ecosystem (e.g., de-duplication across packages) <!-- .element: class="fragment" data-fragment-index="3" -->
</script>
</section>
</div>
</div>
<script src="node_modules/reveal.js/dist/reveal.js"></script>
<script src="node_modules/reveal.js/plugin/markdown/markdown.js"></script>
<script>
Reveal.initialize({
plugins: [ RevealMarkdown ],
center: false,
});
</script>
</body>
</html>