PROMPT
You see request retry rate, directory occupancy, p99 fabric latency on CHI Topology Basics. Walk through root cause and fix.

STRONG ANSWER
1. Names the layer and transaction identity.
2. Explains CHI separates request, response, data, and snoop flows across nodes with directory and home-node responsibilities.
3. Requests CHI node map, VC utilization report, request/response correlation log.
4. Proposes one reduced sequence and one system regression.

WEAK ANSWER
Jumps to widening the interface, increasing FIFO depth, or blaming firmware without evidence.

CHI MESH (RN = request node, HN = home node, SN = slave node)

   RN-F --- X --- X --- RN-I
    |       |     |       |
    X --- HN-F --- X --- X
    |       |     |       |
   SN  --- X --- HN-F --- SN

RN: cores/accelerators that issue requests
HN: home node owns coherency + directory for an address range
SN: memory/peripheral endpoints

Latency = hops x per-hop cost; placement matters.

ROOT-CAUSE TREE — CHI Topology Basics

request retry rate, directory occupancy, p99 fabric latency looks wrong
        |
   reproducible?
     /        \
   no          yes
   |            |
 flaky env   same first transaction every time?
 / seed         /            \
              yes             no
               |               |
        protocol rule     timing/reset/PVT
        or config bug     or load-dependent

COHERENCE TRAFFIC FLOW

RN issues coherent read
   -> HN looks up directory
   -> snoops to sharers
   -> data + state update returned

False sharing: different variables, same cache line -> coherence storm.

COHERENCY TRAFFIC STACK

data fetch        ████████
snoop responses   ██████████████
writebacks        ██████
maintenance ops   ████

High snoop stack with good IPC -> suspect line sharing before faster NoC.