Placement pivot (user-approved): a CUBE Group = C CUBEs within one SIP that
jointly own one KV head + its G=8 query heads. KV sequence sharded 2 levels
(Level-1 inter-CUBE over C, Level-2 intra-CUBE PE over P=8 = C*P ranks); G
folded into matmul M. C is a knob (8/4; C=1 = single-CUBE). Reverses the old
'a query head never spans CUBEs' non-goal (held only because the baseline
was H_kv=1). device=SIP; the for-kv loop is gone (head picked by CUBE coord).
Reduction is a 2-level reduce-to-root (not all-reduce): Level-2 PE tree ->
Level-1 center-root CUBE-mesh reduce, adapting lrab_hierarchical_allreduce's
inter-CUBE pattern as reduce-only + log-sum-exp. Data-driven (send on local
P.V completion, no global barrier) + level-pipelined; per-level topology
configurable (tree for decode, ring for long prefill).
Rewrites SS0/2/4/5/0.5/8-11, pseudocode, and adds SSB items (4-SIP config,
mesh partition, C knob, invariant-reversal check, index-math test). KO mirror
updated. Topology grounded in topology.yaml (4x4 CUBE mesh/SIP, 8 PE/cube).
Docs only; no production code changed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
ywkang
a61fed3ce0