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test(v2): final benchmark campaign - real end-to-end characterization (EXP-0014)

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Post-M10, user-requested final benchmark campaign: 6 realistic
workloads (16-256 independent neurons in a shared-input dense-layer
shape, a random-seeded 2-layer network with real cross-node PSRAM
forwarding, and a 6-node 2-hop dependency diamond) x 4 concurrency
levels (N_SLOTS=1/2/4/8) through the real, full neural_multiprocessor
system (real V1 PSRAM chain, real slot_mem_arbiter). 24/24 runs PASS
bit-exact against a software golden model (11,520 individual neuron/
node checks, zero mismatches).

Three real bugs found and fixed during the campaign itself (ERR-0009):
1. neural_director.v (M5) had a real RTL bug at N_SLOTS=1
   ($clog2(1)=0 makes a replication expression illegal) - never
   caught because M5-M10 only ever tested N_SLOTS=2/4/8. Fixed with
   a width-agnostic '0 literal; M5's own testbench re-verified
   unaffected.
2/3. Two testbench sizing bugs in tb_benchmark_suite.v itself
   (psram_model DEPTH too small for the Large workload's address
   range; N_NODES too small for the Stress workload's node-id range,
   causing a real deadlock via node-id wraparound colliding with an
   already-DISPATCHED node - a real, honest consequence of DEC-0008's
   own "no node-slot reclamation" design choice).

Headline finding: real parallel scaling is essentially flat beyond
N_SLOTS=2 - the single shared PSRAM port saturates at ~91%
utilization regardless of slot count, so memory-bound workloads gain
only 1.05-1.06x real speedup from N=1 to N=8. Once real POST-P&R Fmax
degradation is also factored in, N_SLOTS=4 is measurably 21% SLOWER
in real wall-clock time than N_SLOTS=1 for the largest workload
tested. N_SLOTS=2 is recommended as the default (DEC-0014,
superseding DEC-0012's resource-only "N_SLOTS=8 ceiling" framing for
general use).

Full 21-section report (every number classified THEORETICAL/
SIMULATED/POST-P&R MEASURED/DERIVED, per the user's own
methodology requirements): hardware/v2/docs/benchmarks/
final-benchmark.md

Logged: simulation/synthesis/timing/benchmark/decisions (DEC-0014)/
experiments (EXP-0014)/errors (ERR-0009)/development.log,
ROADMAP.md updated.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
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michele
2026-09-05 19:58:30 +02:00
co-authored by Claude Sonnet 5
parent 91bbbe2fe5
commit 3cdaeaee35
12 changed files with 1369 additions and 4 deletions
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@@ -284,3 +284,30 @@ next_action: nessuna prevista dal mandato (§33 termina a M10) -- la
P_IN<8 per N_SLOTS ancora piu' alto (DEC-0012 alternativa #2), riuso
dei buffer M3 come cache condivisa (DEC-0009), strumentazione
stall%/utilization anche lato V1 (DEC-0011).
[2026-09-05] Final Benchmark Campaign (post-M10, richiesta diretta
utente, non parte del roadmap §33)
reason: caratterizzare le prestazioni reali end-to-end di V2 prima di
decidere il numero finale di unita' parallele (N_SLOTS) e prima di
scrivere il datasheet V2. Nessun test funzionale isolato, nessuna
ottimizzazione prima della misura, come esplicitamente richiesto.
result: 6 workload realistici (16-256 neuroni indipendenti + un layer
multilivello con dati random seed loggato + un DAG a diamante a 2
hop) verificati bit-exact su 4 configurazioni (N_SLOTS=1/2/4/8) --
24/24 PASS dopo aver risolto 3 problemi reali (errors.log ERR-0009).
Scoperta principale: lo scaling parallelo reale e' sostanzialmente
PIATTO per i workload memory-bound (1.05-1.06x da N=1 a N=8) -- il
vero collo di bottiglia e' la porta PSRAM condivisa (~91% utilizzo
indipendentemente da N_SLOTS>=2), non il numero di processori.
Considerando anche il vero Fmax POST-P&R (152.46/142.45/113.38 MHz
per N=1/2/4), N_SLOTS=4 e' realmente PIU' LENTO del 21% in
wall-clock rispetto a N_SLOTS=1 per il workload Stress. Trovato
squilibrio reale di scheduling (slot a indice basso fanno quasi
tutto il lavoro).
errors: vedi errors.log ERR-0009 (1 bug RTL reale in neural_director.v,
mai testato prima a N_SLOTS=1; 2 bug nel testbench stesso).
decision: vedi decisions.log DEC-0014 -- N_SLOTS=2 raccomandato come
configurazione di default, non N_SLOTS=8 (DEC-0012 resta valido come
tetto DSP mafisico, non come raccomandazione d'uso generale).
next_action: datasheet V2 in stile professionale (richiesta utente),
ora sbloccato dalla decisione su N_SLOTS.