Computer Architecture · Cluster
Out-of-Order Execution
Renaming, scheduling, and retirement.
- 01 Why an In-Order Pipeline Stalls and What an Instruction Window Buys How dependencies, latency, and a fixed instruction supply bound an in-order pipeline, and why a sliding window of decoded instructions is the cheapest way out.
- 02 Register Renaming and the Elimination of False Dependencies Why architectural register names serialize otherwise independent code, how a rename table maps names to physical registers, and what the mapping costs in area and latency.
- 03 The Reorder Buffer and In-Order Retirement How entries move through the reorder buffer from allocation to commit, why retirement order is what makes speculative and out-of-order execution safe, and what limits the buffer size.
- 04 Issue Queue Wakeup and Select: The Scheduler Inside the Window How a queue of waiting instructions learns that its operands are ready, how one instruction per port is chosen each cycle, and why the broadcast network is the hard part.
- 05 Load-Store Ordering and Memory Disambiguation in a Speculative Machine Why loads may run ahead of stores, how the memory order buffer checks addresses it does not know yet, and what happens when a load guesses wrong.
- 06 Checkpointing and Recovery from Misprediction How a speculative machine restores an exact rename mapping after a wrong branch, why per-branch checkpoints beat a walk-back repair, and what recovery latency costs.
- 07 Precise Exceptions from an Imprecise Machine Why an out-of-order core must present exceptions at exact instruction boundaries, the ordering rules for synchronous faults versus interrupts, and what the operating system can rely on.
- 08 Front-End Throughput and the Fetch Bandwidth Ceiling Why a wide out-of-order back end can still run narrow, how instruction cache line boundaries, prediction, and decode width bound the supply, and what designs do about it.
- 09 Sizing the Window: Why More Entries Stop Paying The diminishing returns of a larger instruction window, the queueing model that explains them, and the second-order effects that make big windows expensive.
- 10 Value Prediction and the Limits of Speculating on Data What it would take to break true data dependencies, why value prediction attacks a different limit than branch prediction, and the correctness and cost barriers that keep it out of shipping cores.