foxhunt/LLD_SETUP_GUIDE.md

LLD Linker Configuration - Setup Summary

⚠️ Action Required

LLD is not currently installed on this system. Sudo privileges are required for installation.

📋 Quick Setup (Automated)

Run the provided setup script:

sudo bash /tmp/setup_lld.sh

This script will:

1. Install lld package
2. Verify installation
3. Backup current .cargo/config.toml
4. Apply lld configuration
5. Test compilation

📋 Manual Setup (Alternative)

Step 1: Install LLD

sudo apt-get update
sudo apt-get install -y lld

Step 2: Verify Installation

ld.lld --version

Expected output:

LLD 18.x.x (compatible with GNU linkers)

Step 3: Apply Configuration

The updated configuration is ready at: /tmp/config.toml.lld

Copy it to your project:

cp /tmp/config.toml.lld /home/jgrusewski/Work/foxhunt/.cargo/config.toml

Or manually edit /home/jgrusewski/Work/foxhunt/.cargo/config.toml:

Change this section:

[target.x86_64-unknown-linux-gnu]
rustflags = [
    "-C", "link-arg=-Wl,-z,relro,-z,now",
    "-C", "link-arg=-Wl,--as-needed",
    # ... rest of flags

To this:

[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = [
    "-C", "link-arg=-Wl,-z,relro,-z,now",
    "-C", "link-arg=-Wl,--as-needed",
    "-C", "link-arg=-fuse-ld=lld",  # ← ADD THIS LINE
    # ... rest of flags

🧪 Testing After Setup

1. Clean Build Benchmark

cd /home/jgrusewski/Work/foxhunt
cargo clean
time cargo build --release

Record the total time (especially "Linking" phase).

2. Incremental Build Test

# Make a trivial change
echo "// test" >> services/trading_service/src/main.rs
time cargo build --release

3. Load Test Build

time cargo build --bin load_test --release

📊 Expected Results

Before LLD (Baseline)

• Clean build: ~5-10 minutes
• Linking phase: 30-60 seconds
• Incremental build: 20-40 seconds

After LLD (Target)

• Clean build: ~3-6 minutes (40-60% faster)
• Linking phase: 5-15 seconds (70-80% faster)
• Incremental build: 10-20 seconds (50% faster)

Performance Improvements

Metric	Before	After	Improvement
Link time	30-60s	5-15s	70-80%
Clean build	5-10m	3-6m	40-60%
Incremental	20-40s	10-20s	50%

✅ Verification Checklist

After installation and configuration:

• ld.lld --version shows version info
• .cargo/config.toml includes linker = "clang"
• .cargo/config.toml includes "-C", "link-arg=-fuse-ld=lld"
• cargo build --release completes without errors
• Build time is significantly reduced
• Tests still pass: cargo test --workspace
• Binary size is similar to before (±5%)

🔍 Troubleshooting

Issue: "ld.lld: command not found"

Solution: Install lld:

sudo apt-get install -y lld

Issue: "error: linker clang not found"

Solution: Clang is already installed, but verify:

which clang  # Should show /usr/bin/clang

Issue: Build errors after configuration change

Solution: Revert to backup:

cd /home/jgrusewski/Work/foxhunt
cp .cargo/config.toml.backup.* .cargo/config.toml

Issue: No noticeable improvement

Check:

1. Verify lld is actually being used:

cargo build --release -vv 2>&1 | grep -i "link"

Should show clang with -fuse-ld=lld

2. Make sure you're testing release builds (debug builds link faster anyway)

📁 Files Created

1. /tmp/lld_installation_report.md - Detailed analysis and recommendations
2. /tmp/config.toml.lld - Updated configuration file
3. /tmp/setup_lld.sh - Automated setup script
4. /tmp/SETUP_SUMMARY.md - This file

🚀 Next Steps

1. Install lld (requires sudo)
2. Apply configuration (automated or manual)
3. Test builds and measure improvements
4. Report results with before/after timings
5. Update CI/CD to include lld installation
6. Update team docs with new setup requirements

💡 Additional Optimizations

If you want even more build speed:

1. Use cargo-nextest for parallel testing
2. Enable sccache for shared compilation cache
3. Use cargo-chef for Docker layer caching
4. Configure ramdisk for target directory (advanced)

📚 Resources

• LLD Documentation: https://lld.llvm.org/
• Rust Linker Configuration: https://doc.rust-lang.org/cargo/reference/config.html
• Foxhunt .cargo/config.toml: /home/jgrusewski/Work/foxhunt/.cargo/config.toml