RISC-V Design · All levels
RVV Vector Basics: Interview Drills
Interview Drills for RVV Vector Basics.
Interview drills
Interview Drills for RVV Vector Basics is anchored on Sustained vector utilization across mixed-width kernels while keeping scalar fallback correctness intact.. Convert observations into mechanism-backed decisions with explicit ownership.
diagram
PROMPT
You observe Sustained vector utilization across mixed-width kernels while keeping scalar fallback correctness intact. on RVV Vector Basics. Walk through root cause and release decision.
STRONG ANSWER
1. Defines workload and earliest failing mechanism.
2. Explains mechanism: RVV decouples architectural vector length from implementation width through vtype and vl, so software scales across cores with different VLEN values. Hardware executes vector instructions over available lanes with tail and mask semantics preserving deterministic behavior when loop trip counts are not multiples of lane width. Correct implementation requires precise exception behavior, clear scalar-vector state transitions, and stable save-restore of vector CSRs across interrupts and context switches.
3. Requests proving artifact: Vector bring-up checklist covering vtype/vl programming, tail/mask policy, context-switch state, and scalar fallback tests.
4. Proposes bounded fix + owner + rollback-safe validation.
WEAK ANSWER
Suggests generic optimization ideas without mechanism proof or owner accountability.Decision matrix
diagram
RISC-V EVIDENCE MATRIX - RVV Vector Basics
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence | Tells you | Does not prove | Next action |
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| perf counter timeline | where regression appears | exact mechanism causality | correlate with trace |
| decode/control dump | control intent per instruction | pipeline side-effect ordering | inspect retire semantics |
| trap + CSR logs | privilege/fault behavior | performance bottleneck alone | pair with CPI buckets |
| MMU/TLB walk trace | translation behavior | full system QoS impact | test mixed workloads |
| post-fix trend graph | movement after fix | long-term stability | run stress matrix |
+--------------------------+--------------------------------+--------------------------------+---------------------------+