Thoughts, terms, and ideas I’ve come across over the last few months.

• Tail call benefit - Callee is using the same stack space as caller which reduces memory pressure and makes it more likely that chunk of the stack will stay in the CPU cache.
• Cores are black boxes that instructions enter and leave from in a sequential manner. Inside the black box instructions can run in any order.
• Out of order execution
  • Fetch multiple instructions each cycle and decode into µ-ops.
  • µ-ops are put into the re-order buffer (ROB) where they can be processed out of order if data is ready.
  • To prevent pipeline stalls speculative execution runs all the conditional branches in parallel until the core figures out which branch to take.
• Hyperthreading - Provides two virtual processors that share a reorder buffer. Provides the core with more data during general workloads to keep execution units busy.
• Pipelines improve performance but can cause nightmares if they stall!
  • CPUs run best when instructions and data are in order.
  • Keep data in order, adjacent, and consecutive to prevent data stalls.
  • Don’t jump around because it won’t be able to predict where you want to go.
  • Take comparisons out of loops to prevent mispredicted branches. For { If { … } } => If { For { … } }
• Think about the period of time when we are waiting for followers to acknowledge a write as your uncertainty window. As followers acknowledge the write we are increasingly certain that our write has been captured and eventually we can advance our uncertainty window.