benchmarking-optimization

name	Benchmarking & Optimization
description	This skill should be used when the user asks to "run benchmarks", "profile performance", "measure allocations", "optimize render speed", "find hot paths", "generate flamegraph", or mentions stackprof, memory profiler, or performance optimization.

LiquidIL Benchmarking & Optimization

Guide for measuring and improving LiquidIL render performance.

Running Benchmarks

Official Benchmark Suite (Primary)

rake bench

Runs 11 real-world templates comparing liquid_ruby, liquid_il (VM), liquid_il_compiled, and liquid_il_optimized_compiled. Shows compile time, render time, and speedup ratios.

Partials Microbenchmark (with allocations)

bundle exec ruby bench_partials.rb

Focused on partial rendering performance with allocation tracking. Useful for optimizing isolated scope / render tag performance.

bundle exec ruby bench_partials.rb --iterations 100    # Quick runs
bundle exec ruby bench_partials.rb --help              # All options

Profiling

CPU Profiling with Stackprof

Profile all benchmarks:

bundle exec ruby bench_partials.rb --profile stackprof --iterations 500

Profile a specific benchmark (recommended for focused analysis):

bundle exec ruby bench_partials.rb --profile stackprof --profile-benchmark bench_ecommerce_product_page --iterations 1000

View results:

bundle exec stackprof tmp/stackprof_*.dump --text --limit 30

Drill into a specific method:

bundle exec stackprof tmp/stackprof_*.dump --method 'ClassName#method_name'

Generate flamegraph:

bundle exec stackprof tmp/stackprof_*_liquid_il.dump --d3-flamegraph > tmp/flamegraph.html
open tmp/flamegraph.html

Memory Profiling

bundle exec ruby bench_partials.rb --profile memory --profile-benchmark bench_ecommerce_product_page --iterations 100

Results saved to tmp/memory_*.txt.

Render-Only Profiling

For profiling just the render phase (excluding compile time):

bundle exec ruby profile_render.rb

Interpreting Stackprof Output

==================================
  Mode: wall(100)
  Samples: 2866 (0.00% miss rate)
  GC: 231 (8.06%)              <- GC overhead, lower is better
==================================
     TOTAL    (pct)     SAMPLES    (pct)     FRAME
       531  (18.5%)         362  (12.6%)     #<Module:...>#__write_output__

• TOTAL: Time in method + everything it calls
• SAMPLES (self): Time directly in that method
• High TOTAL, low self → optimize callees
• High self → optimize this method directly

Optimization Workflow

1. Establish baseline: Run bench_partials.rb to get current numbers
2. Profile hot path: Use stackprof to identify time sinks
3. Identify targets: Look for high self% methods
4. Apply optimization patterns (see below)
5. Verify improvement: Re-run benchmarks and compare

Optimization Patterns

Replace Hash Lookups with Direct Ivars

Before:

def capturing? = registers["capture_stack"].any?

After:

def initialize
  @capture_stack = []  # Eager init
end
def capturing? = !@capture_stack.empty?

Avoid respond_to? for Common Types

Before:

def output_string(value)
  value = value.to_liquid if value.respond_to?(:to_liquid)
  # ...
end

After:

def output_string(value)
  case value
  when String then value
  when Integer, Float then value.to_s
  when nil then ""
  else
    value = value.to_liquid if value.respond_to?(:to_liquid)
    to_s(value)
  end
end

Eager vs Lazy Initialization

• Hot-path arrays: Initialize eagerly as ivars
• Rarely-used hashes: Lazy init with ||=

Key Files

File	Purpose
bench_partials.rb	Main benchmark runner with allocation tracking
profile_render.rb	Focused render-only profiling
benchmarks/partials.yml	Benchmark test cases
lib/liquid_il/context.rb	RenderScope (hot path for partials)
lib/liquid_il/utils.rb	output_string, to_s (called on every output)
lib/liquid_il/ruby_compiler.rb	write_output and compiled helpers

Performance Targets

• Speedup vs liquid_ruby: 2x+ on complex templates
• Allocations: Comparable or fewer than liquid_ruby
• GC pressure: Keep under 10% of profile samples