faster_build_times.md

1. Faster incremental builds (6s instead of 40s)
2. Faster clean builds with 'sccache' (3min instead of 7min)

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1. Faster incremental builds (6s instead of 40s)

Here are some configs and experiment results for Ubuntu and macOS faster build times.
Hint: Search for "FASTEST"

Ubuntu 20.04 - ~5x faster incremental builds:

cargo b tower

    // default 
    Full build: 7m
    Incr build: 30-54s
    Bin Size  : 558 MB    

    // w/ [build] rustflags = ["-C", "link-arg=-fuse-ld=lld"]    
    Full build: 6:11
    Incr build: 6-7s
    Bin Size  : 567 MB          
    
    [FASTEST]
    // w/ 1) # disable debug symbols for all packages except this one 
          2) [build] rustflags = ["-C", "link-arg=-fuse-ld=lld"]    
    Full build: 4:31
    Incr build: 5-6s
    Bin Size  : 372 MB   

    // w/ 1) [build] rustflags = ["-C", "link-arg=-Wl,--compress-debug-sections=zlib-gabi"]
          2) # Optimize all dependencies for small size
    Full build: 
    Incr build: 43s - 1:20
    Bin Size  : 182 MB

Related Configs:

.cargo/config (Note: sudo apt-get install lld)
# Dramatically increases the link performance for the eventbus
[build]
rustflags = ["-C", "link-arg=-fuse-ld=lld"]   

root cargo.toml 
[profile.dev.package."*"]
# disable debug symbols for all packages except this one
debug = false
   
root cargo.toml 
# Optimize all dependencies for small size
[profile.dev.package."*"]
opt-level = "z"

.cargo/config
[build]
# Compress debug sections for small size
rustflags = ["-C", "link-arg=-Wl,--compress-debug-sections=zlib-gabi"]

macOS (MacBook Pro Mid 2015) - 5x faster incremental builds:

cargo b tower

    // default 
    Full build: 5:58
    Incr build: 38sec

    // w/ # disable debug symbols for all packages except this one 
    Full build: 4:57
    Incr build: 23sec

    [FASTEST w/ rust 1.46 - current 0L default version]
    // w/ 1) [build] rustflags = ["-C", "link-arg=-fuse-ld=zld"]
          2) # disable debug symbols for all packages except this one
    Full build: 4:32
    Incr build: 19s    

    // rust 1.51 default
    Full build: 7:55
    Incr build: 40s
    
    // rust 1.51 + split-debuginfo = "unpacked"
    Full build: 7:00
    Incr build: 12s

    [FASTEST w/ rust 1.51]
    // rust 1.51 + 
          1) split-debuginfo = "unpacked"
          2) [build] rustflags = ["-C", "link-arg=-fuse-ld=zld"]
          3) # disable debug symbols for all packages except this one    
    Full build: 6:15
    Incr build: 7s

Related Configs:

.cargo/config
[build] 
rustflags = ["-C", "link-arg=-fuse-ld=zld"]

root cargo.toml 
[profile.dev]
split-debuginfo = "unpacked" # Requires rustc 1.51

root cargo.toml 
[profile.dev.package."*"]
# disable debug symbols for all packages except this one
debug = false

2. Faster clean builds with 'sccache' (3min instead of 7min)

see also: (Improve-Rust-compile-times-with-sccache.md)

Measure your build time first without 'sccache':

// Clean build of `tower` takes around 7min
cargo clean 
cargo b -p tower 

Setup

cargo install sccache
echo "export RUSTC_WRAPPER=sccache" >> ~/.bashrc
source ~/.bashrc

// macos 
echo "export RUSTC_WRAPPER=sccache" >> ~/.profile
source ~/.profile  

Use sccache

// Ignore this build - caching here
cargo clean 
cargo b -p tower 

// Now, this takes `3min` instead of `7min` - Incredible!
cargo clean 
cargo b -p tower