RISC-V Design · All levels

Performance Tuning and Signoff: Theory Deep Dive

Theory Deep Dive for Performance Tuning and Signoff.

Theory deep dive

Theory Deep Dive for Performance Tuning and Signoff is anchored on P95 and P99 workload latency, sustained throughput per subsystem, and power-performance target closure against signoff criteria.. Convert observations into mechanism-backed decisions with explicit ownership.

Theory matters when it predicts engineering outcomes. Tie abstract ISA and microarchitecture concepts to measurable behavior in trace and counter data.

Pipeline model

diagram

RISC-V PIPELINE DIAGRAM - Performance Tuning and Signoff

PC -> IF -> ID -> EX -> MEM -> WB
      |     |      |      |      |
  i-cache decode  ALU/BR  LSU    regfile write
              \   |
               +-> branch resolve + redirect

Hot paths:
  - branch + load-use dependencies in ID/EX
  - memory latency stretching MEM stage
  - writeback arbitration for integer/vector units

Focus: keep control hazards predictable

Privilege model

diagram

PRIVILEGE MODE STACK - Performance Tuning and Signoff

            +------------------------------+
            | Machine mode (M)             |
            | firmware, PMP, trap root     |
            +---------------+--------------+
                            |
                    delegated traps
                            v
            +------------------------------+
            | Supervisor mode (S)          |
            | kernel, page tables, drivers |
            +---------------+--------------+
                            |
                    ecall / syscall
                            v
            +------------------------------+
            | User mode (U)                |
            | applications, libraries      |
            +------------------------------+

Key rule: each upward transition records cause + PC in trap CSRs.

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