monoruby is a new Ruby implementation I am working on, written in Rust, built from scratch, and consisting of a parser, interpreter, garbage collector, and just-in-time (JIT) compiler. Since the last RubyKaigi, I have made progress in Rubygems support and other performance improvements. This time I want to present the details of the optimizations and the various features for performance tuning. Meaningful optimization requires measurement and evaluation, so I have implemented features to record where and why various events such as JIT compilation, JIT code invalidation, and deoptimization (back to the interpreter) occurred, and to display the generated assembly for each virtual machine instruction. The actual optimizations implemented in monoruby include machine code inlining, method inlining, polymorphic method call optimization, faster instance variable access, faster array access, etc. Making the Ruby compiler is fun.