analytical-viz: autosuggest prefers fewer cubes, tries cp_placement=pe

Two changes to the memory-only auto_suggest so a "fits" that packs into
one cube is preferred over a "fits" that spreads across multiple cubes.

Suggestion dataclass gains cubes_used and cp_placement fields.

_score_candidate: for each (CP,TP,PP) triple, try cp_placement="cube"
(historical default: CP spans cubes) and, when CP·TP fits in one cube's
PE count, also cp_placement="pe" (pack CP into intra-cube PEs). Keep
the placement with fewer cubes; break ties toward "cube".

auto_suggest: switch sort key from (pes_used ↑, pp ↑, tp ↑, cp ↑) to
(cubes_used ↑, pes_used ↑, pp ↑, tp ↑, cp ↑). Fewer cubes wins first
because a cube is the physical die-level unit; PE count is the
tiebreaker.

Sidebar caption now also displays cubes_used + cp_placement so the
user can see the packed layout at a glance. Preset-change auto-reset
also applies the picked cp_placement.

Observed effect (verified):
  Qwen 3 8B / 128K decode:  CP=4 TP=2, "pe" → 1 cube, 8 PEs
                             (was 4 cubes with default "cube")
  Llama 3.1 70B / 128K:      CP=4 TP=16, "cube" → 8 cubes (unchanged;
                             TP=16 > 8 PEs/cube, can't pack)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/analytical_visualization/autosuggest.py

@@ -32,6 +32,8 @@ class Suggestion:
     fits: bool
     pes_used: int
     sips_used: int
+    cubes_used: int = 0            # picked to minimize this (see _score_candidate)
+    cp_placement: str = "cube"     # "pe" packs CP into intra-cube PEs when it fits
     reason: str = ""
 
 
@@ -59,7 +61,25 @@ def _score_candidate(cp: int, tp: int, pp: int,
                      model: ModelConfig, machine: MachineParams,
                      s_kv: int, mode: str,
                      slack_frac: float = 0.10) -> Suggestion:
-    topo = TopologyConfig(cp=cp, tp=tp, pp=pp, s_kv=s_kv, mode=mode)
+    # For each triple, try both cp_placement options and keep the one
+    # with fewer cubes (breaks the historical "CP always across cubes"
+    # default when a smaller pack is possible). The pe placement is only
+    # valid when CP·TP fits within a single cube's PE count.
+    best_topo: TopologyConfig | None = None
+    best_placement = "cube"
+    _pe_per_cube_hw = TopologyConfig().pes_per_cube_hw  # instance-invariant HW const
+    _placements_to_try = ["cube"]
+    if cp * tp <= _pe_per_cube_hw:
+        _placements_to_try.append("pe")
+    for _place in _placements_to_try:
+        _t = TopologyConfig(
+            cp=cp, tp=tp, pp=pp, s_kv=s_kv, mode=mode,
+            cp_placement=_place,
+        )
+        if best_topo is None or _t.cubes_used < best_topo.cubes_used:
+            best_topo = _t
+            best_placement = _place
+    topo = best_topo
     cfg = FullConfig(model=model, topo=topo, machine=machine)
     mem = compute_memory(cfg)
 
@@ -80,6 +100,8 @@ def _score_candidate(cp: int, tp: int, pp: int,
         fits=fits,
         pes_used=topo.total_pes,
         sips_used=topo.sips_used,
+        cubes_used=topo.cubes_used,
+        cp_placement=best_placement,
         reason=reason,
     )
 
@@ -87,20 +109,27 @@ def _score_candidate(cp: int, tp: int, pp: int,
 def auto_suggest(model: ModelConfig, machine: MachineParams,
                  s_kv: int, mode: str = "decode",
                  slack_frac: float = 0.10) -> Suggestion:
-    """Return the smallest-PE-count (CP, TP, PP) that fits.
+    """Return the smallest deployment (fewer cubes, then fewer PEs)
+    that fits.
+
+    Sort key: (cubes_used ↑, pes_used ↑, pp ↑, tp ↑, cp ↑).
+    Fewer cubes wins first because a cube is the physical die-level
+    hardware unit; PE count is the tiebreaker. Preferring fewer PP then
+    TP then CP keeps the earlier historical bias (avoid pipeline
+    bubbles / head-dim splits) among equal-cube-and-PE ties.
 
     If no candidate fits, returns the best-effort one (highest slack,
     even if negative) with fits=False.
     """
-    best_fit: Suggestion | None = None
-    best_effort: Suggestion | None = None
-
+    scored: list[Suggestion] = []
     for cp, tp, pp in _iter_candidates(model):
-        s = _score_candidate(cp, tp, pp, model, machine, s_kv, mode, slack_frac)
-        if s.fits and best_fit is None:
-            best_fit = s
-            break  # candidates are pre-sorted by PE count
-        if best_effort is None or s.slack_gb > best_effort.slack_gb:
-            best_effort = s
+        scored.append(
+            _score_candidate(cp, tp, pp, model, machine, s_kv, mode, slack_frac)
+        )
+    scored.sort(key=lambda s: (s.cubes_used, s.pes_used, s.pp, s.tp, s.cp))
 
-    return best_fit or best_effort  # type: ignore
+    for s in scored:
+        if s.fits:
+            return s
+    # No fit — return the best-effort (largest slack, closest to fitting).
+    return max(scored, key=lambda s: s.slack_gb)