nvfp4-megamoe-kernel/tests/archive/test_decode_attention_b200.py

#!/usr/bin/env python3
"""
DeepSeek-V4 Decode Attention Pipeline Test

REPRODUCES THE BUG: The vLLM Blackwell path uses raw KV for attention,
which means decode (generating token N+1 when tokens 0..N are in the KV cache)
produces garbage because the cache is never written to.

This test simulates the actual decode scenario:
1. Prefill: compute KV for N tokens, write to paged cache
2. Decode: compute KV for 1 new token, write to cache, then attend to ALL cached KV

The key insight: during decode, you can't use raw KV — you need the KV cache
because previous tokens' KV was computed in a prior forward pass.

Architecture:
- KV latent is (T, 512) — single head, shared across all 128 Q heads
- After kv_norm + RoPE, KV is quantized to fp8 and stored in paged cache
- Attention: Q (128 heads) × K^T → softmax → × V
- For CSA/HCA: attention attends to compressed positions (every 4th or 128th)
- For SWA: attention attends to last WINDOW tokens

Usage (on B200):
  cd /root/nvfp4-megamoe-kernel
  PYTHONPATH=/root/nvfp4-megamoe-kernel tests/venv/bin/python tests/test_decode_attention_b200.py
"""

import sys, os, json, torch, torch.nn.functional as F, math
from safetensors import safe_open

REPO = "/root/nvfp4-megamoe-kernel"
sys.path.insert(0, REPO)
MODEL = "/root/nvidia-meeting/DeepSeek-V4-Pro-NVFP4"
DEV = "cuda:0"

H = 7168; NH = 128; HD = 512; NOPE = 448; ROPE = 64
QL = 1536; OL = 1024; OG = 16; HPG = NH // OG
EPS = 1e-6; WINDOW = 128; SCALE = HD ** -0.5

E2M1 = torch.tensor([0,.5,1.,1.5,2.,3.,4.,6.,-0,-.5,-1.,-1.5,-2.,-3.,-4.,-6.], dtype=torch.float32)

_cache = {}
def P(k, wm, md):
    if k in _cache: return _cache[k]
    with safe_open(os.path.join(md, wm[k]), framework="pt") as f:
        t = f.get_tensor(k)
    _cache[k] = t
    return t

def dequant(w, sf, gs):
    d = w.device; lut = E2M1.to(d)
    lo = lut[(w & 0xF).long()]; hi = lut[((w >> 4) & 0xF).long()]
    O, I2 = w.shape; I = I2*2
    u = torch.empty(O, I, dtype=torch.float32, device=d)
    u[:,0::2] = lo; u[:,1::2] = hi
    bs = sf.float().repeat_interleave(16, dim=1)[:O,:I]
    return (u * bs * gs).to(torch.bfloat16)

def rms(x, w, eps=1e-6):
    v = x.float().pow(2).mean(-1, keepdim=True)
    return (w.float() * (x * torch.rsqrt(v+eps)).float()).to(x.dtype)

def make_runner(w, sf, gs_t, inf, outf, fused=False, lw=None):
    from dsv4.layers.linear import Nvfp4Linear
    fp4 = w.view(torch.float4_e2m1fn_x2).permute(1,0).contiguous()
    s = sf.to(torch.float8_e4m3fn) if sf.dtype != torch.float8_e4m3fn else sf
    s = s.permute(1,0).contiguous()
    if fused and gs_t.numel() == 2:
        g1,g2 = gs_t[0].item(), gs_t[1].item(); gs = max(g1,g2)
        if g1 != g2:
            s32 = s.float(); sp = lw[0] if lw else outf//2
            s32[:sp] *= g1/gs; s32[sp:] *= g2/gs; s = s32.to(torch.float8_e4m3fn)
    else:
        gs = gs_t.max().item() if gs_t.numel() > 1 else gs_t.item()
    r = Nvfp4Linear(in_features=inf, out_features=outf, max_num_tokens=8192, device=str(w.device))
    r.fp4 = [fp4]; r.sf = [s]; r.gs = [gs]
    r.finalize_weights(); r._ensure_initialized()
    return r

def build_cos_sin(max_pos=4096, rope_dim=ROPE):
    half = rope_dim // 2
    inv_freq = 1.0 / (10000.0 ** (torch.arange(0, half, dtype=torch.float32) / half))
    freqs = torch.outer(torch.arange(max_pos, dtype=torch.float32), inv_freq)
    return torch.cat([freqs.cos(), freqs.sin()], dim=-1)

def apply_gptj_rope(x, positions, cos_sin, nope, rope):
    if rope == 0 or x.numel() == 0: return x
    half = rope // 2
    cos = cos_sin[positions, :half].to(x.dtype)
    sin = cos_sin[positions, half:2*half].to(x.dtype)
    if x.dim() == 3: cos = cos.unsqueeze(1); sin = sin.unsqueeze(1)
    x_rope = x[..., nope:].clone()
    even = x_rope[..., 0::2]; odd = x_rope[..., 1::2]
    out = x.clone()
    out[..., nope:][..., 0::2] = even * cos - odd * sin
    out[..., nope:][..., 1::2] = even * sin + odd * cos
    return out

def apply_inv_gptj_rope(x, positions, cos_sin, nope, rope):
    if rope == 0 or x.numel() == 0: return x
    half = rope // 2
    cos = cos_sin[positions, :half].to(x.dtype)
    sin = cos_sin[positions, half:2*half].to(x.dtype)
    if x.dim() == 3: cos = cos.unsqueeze(1); sin = sin.unsqueeze(1)
    x_rope = x[..., nope:].clone()
    even = x_rope[..., 0::2]; odd = x_rope[..., 1::2]
    out = x.clone()
    out[..., nope:][..., 0::2] = even * cos + odd * sin
    out[..., nope:][..., 1::2] = -even * sin + odd * cos
    return out


# ── KV Cache Kernels ────────────────────────────────────────────────

def kv_quantize_fp8(kv_bf16):
    """BF16 KV → fp8_e4m3 with per-token scale."""
    amax = kv_bf16.float().abs().amax(dim=-1, keepdim=True).clamp(min=1e-12)
    fp8_max = torch.tensor(448.0, dtype=torch.float32, device=kv_bf16.device)
    scale = fp8_max / amax
    kv_fp8 = (kv_bf16.float() * scale).to(torch.float8_e4m3fn)
    inv_scale = (amax / fp8_max).to(torch.bfloat16)
    return kv_fp8, inv_scale

def kv_dequantize_fp8(kv_fp8, inv_scale):
    """fp8 KV → BF16."""
    return (kv_fp8.to(torch.bfloat16) * inv_scale).to(torch.bfloat16)

def paged_kv_write(kv_data, slot_mapping, cache, block_size):
    """Write data into paged cache. Works for fp8 or bf16.
    
    kv_data: (T, D) tensor to write
    slot_mapping: (T,) slot indices
    cache: (num_blocks, block_size, D) cache tensor
    """
    for t in range(kv_data.shape[0]):
        slot = slot_mapping[t].item()
        block_idx = slot // block_size
        offset = slot % block_size
        if block_idx < cache.shape[0] and offset < cache.shape[1]:
            cache[block_idx, offset] = kv_data[t]

def paged_kv_read(slot_mapping, cache, block_size, num_tokens, head_dim):
    """Read KV from paged cache."""
    device = cache.device
    kv = torch.zeros(num_tokens, head_dim, dtype=cache.dtype, device=device)
    for t in range(num_tokens):
        slot = slot_mapping[t].item()
        block_idx = slot // block_size
        offset = slot % block_size
        if block_idx < cache.shape[0] and offset < cache.shape[1]:
            kv[t] = cache[block_idx, offset]
    return kv


# ── Attention ────────────────────────────────────────────────────────

def full_causal_attention(q, kv, scale):
    """Full causal self-attention. q: (T_q, NH, HD), kv: (T_kv, HD).
    
    Works for prefill (T_q == T_kv) and decode (T_q == 1, T_kv > 1).
    Uses SDPA for efficiency.
    """
    T_q, NH, HD = q.shape
    T_kv = kv.shape[0]
    
    # q: (NH, T_q, HD), k/v: (NH, T_kv, HD) — shared KV across heads
    q_t = q.permute(1, 0, 2)  # (NH, T_q, HD)
    kv_exp = kv.unsqueeze(0).expand(NH, -1, -1)  # (NH, T_kv, HD)
    v_exp = kv_exp.clone()
    
    # Causal mask: query at position i can attend to positions <= i
    # For decode (T_q=1), all T_kv positions are valid (position T_kv-1 attends to 0..T_kv-1)
    if T_q == T_kv:
        # Prefill: standard causal
        attn_mask = torch.tril(torch.ones(T_q, T_kv, device=q.device, dtype=torch.bool)).unsqueeze(0).expand(NH, -1, -1)
        out = F.scaled_dot_product_attention(q_t, kv_exp, v_exp, attn_mask=attn_mask, scale=scale)
    else:
        # Decode or mixed: no masking needed (all positions are in the past)
        out = F.scaled_dot_product_attention(q_t, kv_exp, v_exp, is_causal=False, scale=scale)
    
    return out.permute(1, 0, 2)  # (T_q, NH, HD)


def swa_decode_attention(q_new, kv_cache_bf16, positions_new, scale, window_size=WINDOW):
    """Decode-time sliding window attention.
    
    q_new: (1, NH, HD) — single new query token with RoPE
    kv_cache_bf16: (total_len, HD) — ALL cached KV (already with RoPE)
    positions_new: (1,) — position of the new token
    """
    total_len = kv_cache_bf16.shape[0]
    pos = positions_new[0].item()
    window_start = max(0, pos - window_size + 1)
    window_len = pos - window_start + 1
    
    # Get the KV window
    kv_window = kv_cache_bf16[window_start:pos+1]  # (window_len, HD)
    NH = q_new.shape[1]
    HD = q_new.shape[2]
    
    # Multi-head attention
    q_2d = q_new.reshape(NH, HD)  # (NH, HD)
    k_exp = kv_window.unsqueeze(0).expand(NH, -1, -1)  # (NH, window_len, HD)
    v_exp = k_exp.clone()
    
    # scores: (NH, 1, window_len)
    scores = torch.matmul(q_2d.unsqueeze(1), k_exp.transpose(-1, -2)) * scale
    weights = F.softmax(scores.float(), dim=-1).to(q_new.dtype)
    out = torch.matmul(weights, v_exp).squeeze(1)  # (NH, HD)
    return out.unsqueeze(0)  # (1, NH, HD)


def test_prefill_decode(layer_id, compress_ratio):
    """Test the full prefill + decode attention pipeline.
    
    Simulates what vLLM actually does:
    1. PREFILL: Process N tokens, write their KV to the paged cache
    2. DECODE: Process 1 new token, write its KV to the cache, attend to all cached KV
    
    Compares decode output against a full BF16 reference (which processes all tokens at once).
    """
    torch.cuda.set_device(0)
    torch.manual_seed(42)
    torch.cuda.empty_cache()
    
    with open(os.path.join(MODEL, "model.safetensors.index.json")) as f:
        wm = json.load(f)["weight_map"]
    G = lambda k: P(k, wm, MODEL).to(DEV)
    
    p = f"model.layers.{layer_id}"; a = f"{p}.self_attn"
    layer_type = "SWA" if compress_ratio <= 1 else f"CSA(c={compress_ratio})"
    
    print(f"\n{'='*70}")
    print(f"  Layer {layer_id} — {layer_type} — Prefill+Decode Test")
    print(f"{'='*70}")
    
    # Load weights
    emb = G("model.embed_tokens.weight")
    anorm = G(f"{p}.input_layernorm.weight")
    qn = G(f"{a}.q_a_norm.weight"); kvn = G(f"{a}.kv_norm.weight")
    woa = G(f"{a}.o_a_proj.weight")
    
    qa_w = G(f"{a}.q_a_proj.weight"); qa_sf = G(f"{a}.q_a_proj.weight_scale"); qa_gs = G(f"{a}.q_a_proj.weight_scale_2")
    qb_w = G(f"{a}.q_b_proj.weight"); qb_sf = G(f"{a}.q_b_proj.weight_scale"); qb_gs = G(f"{a}.q_b_proj.weight_scale_2")
    kv_w = G(f"{a}.kv_proj.weight"); kv_sf = G(f"{a}.kv_proj.weight_scale"); kv_gs = G(f"{a}.kv_proj.weight_scale_2")
    wob_w = G(f"{a}.o_b_proj.weight"); wob_sf = G(f"{a}.o_b_proj.weight_scale"); wob_gs = G(f"{a}.o_b_proj.weight_scale_2")
    
    # CuTeDSL runners
    r_qa = make_runner(qa_w, qa_sf, qa_gs, H, qa_w.shape[0])
    r_qb = make_runner(qb_w, qb_sf, qb_gs, QL, qb_w.shape[0])
    r_kv = make_runner(kv_w, kv_sf, kv_gs, H, kv_w.shape[0])
    r_wob = make_runner(wob_w, wob_sf, wob_gs, OG*OL, wob_w.shape[0])
    
    # Setup
    N_PREFILL = 8   # Number of prefill tokens
    N_DECODE = 1    # Single decode token
    N_TOTAL = N_PREFILL + N_DECODE
    
    token_ids = torch.tensor([1, 450, 8403, 315, 5413, 374, 2198, 643, 991], dtype=torch.long, device=DEV)
    assert len(token_ids) >= N_TOTAL
    cos_sin = build_cos_sin(max_pos=4096).to(DEV)
    
    # Paged KV cache
    block_size = 256
    num_blocks = 64
    # Cache stores fp8 KV (with per-token inv_scale stored separately)
    kv_cache_fp8 = torch.zeros(num_blocks, block_size, HD, dtype=torch.float8_e4m3fn, device=DEV)
    # Per-token inv scales (indexed by slot)
    inv_scale_cache = torch.zeros(num_blocks * block_size, 1, dtype=torch.bfloat16, device=DEV)
    # RoPE'd BF16 KV cache (for reference — in production, RoPE is applied after dequant)
    kv_cache_bf16 = torch.zeros(N_TOTAL, HD, dtype=torch.bfloat16, device=DEV)
    
    with torch.no_grad():
        # ════════════════════════════════════════════════════════════════
        # STEP 1: PREFILL — process tokens 0..N_PREFILL-1
        # ════════════════════════════════════════════════════════════════
        prefill_ids = token_ids[:N_PREFILL]
        prefill_pos = torch.arange(N_PREFILL, dtype=torch.int64, device=DEV)
        prefill_slots = prefill_pos  # slot = position (simplified)
        
        hidden_prefill = emb[prefill_ids]
        normed_prefill = rms(hidden_prefill, anorm, EPS)
        
        # Project KV
        kv_prefill = r_kv.run(normed_prefill)
        kv_normed_prefill = rms(kv_prefill, kvn, EPS)
        
        # Apply RoPE to KV BEFORE caching
        kv_rope_prefill = apply_gptj_rope(kv_normed_prefill.unsqueeze(1), prefill_pos, cos_sin, NOPE, ROPE).squeeze(1)
        
        # Quantize to fp8
        kv_fp8_prefill, inv_scale_prefill = kv_quantize_fp8(kv_rope_prefill)
        
        # Write to paged cache
        paged_kv_write(kv_fp8_prefill, prefill_slots, kv_cache_fp8, block_size)
        # Write inv_scale to flat cache
        for t in range(N_PREFILL):
            slot = prefill_slots[t].item()
            inv_scale_cache[slot] = inv_scale_prefill[t]
        
        # Also store BF16 reference (for verification)
        kv_cache_bf16[:N_PREFILL] = kv_rope_prefill
        
        print(f"  Prefill: {N_PREFILL} tokens written to KV cache")
        print(f"  KV cache fp8 amax: {kv_fp8_prefill.float().abs().max():.4f}")
        print(f"  KV BF16 amax: {kv_rope_prefill.amax():.4f}")
        
        # Verify roundtrip: read back and compare
        kv_read = paged_kv_read(prefill_slots, kv_cache_fp8, block_size, N_PREFILL, HD)
        inv_read = inv_scale_cache[prefill_slots]
        kv_dequant = kv_dequantize_fp8(kv_read, inv_read)
        c = F.cosine_similarity(kv_rope_prefill.flatten().unsqueeze(0).float(), kv_dequant.flatten().unsqueeze(0).float()).item()
        print(f"  KV cache roundtrip cosine: {c:.6f} {'✅' if c>=0.99 else '❌'}")
        
        # ════════════════════════════════════════════════════════════════
        # STEP 2: DECODE — process token N_PREFILL
        # ════════════════════════════════════════════════════════════════
        decode_id = token_ids[N_PREFILL:N_PREFILL + N_DECODE]
        decode_pos = torch.tensor([N_PREFILL], dtype=torch.int64, device=DEV)
        decode_slot = decode_pos
        
        hidden_decode = emb[decode_id]
        normed_decode = rms(hidden_decode, anorm, EPS)
        
        # Project Q and KV
        qa_decode = r_qa.run(normed_decode)
        kv_decode = r_kv.run(normed_decode)
        qa_n_decode = rms(qa_decode, qn, EPS)
        kv_n_decode = rms(kv_decode, kvn, EPS)
        q_decode = r_qb.run(qa_n_decode).view(N_DECODE, NH, HD)
        q_rope_decode = apply_gptj_rope(q_decode, decode_pos, cos_sin, NOPE, ROPE)
        
        # Apply RoPE to KV
        kv_rope_decode = apply_gptj_rope(kv_n_decode.unsqueeze(1), decode_pos, cos_sin, NOPE, ROPE).squeeze(1)
        
        # Write decode KV to cache
        kv_fp8_decode, inv_scale_decode = kv_quantize_fp8(kv_rope_decode)
        paged_kv_write(kv_fp8_decode, decode_slot, kv_cache_fp8, block_size)
        for t in range(N_DECODE):
            slot = decode_slot[t].item()
            inv_scale_cache[slot] = inv_scale_decode[t]
        kv_cache_bf16[N_PREFILL:N_PREFILL + N_DECODE] = kv_rope_decode
        
        print(f"\n  Decode: token {N_PREFILL} written to KV cache")
        
        # ════════════════════════════════════════════════════════════════
        # STEP 3: DECODE ATTENTION using KV cache
        # ════════════════════════════════════════════════════════════════
        
        # Read ALL KV from cache (tokens 0..N_PREFILL)
        all_slots = torch.arange(N_TOTAL, dtype=torch.int64, device=DEV)
        kv_all_fp8 = paged_kv_read(all_slots, kv_cache_fp8, block_size, N_TOTAL, HD)
        inv_scale_all = inv_scale_cache[all_slots]
        kv_all_dequant = kv_dequantize_fp8(kv_all_fp8, inv_scale_all)
        
        # SWA: attend to last WINDOW tokens (or all if total < WINDOW)
        if N_TOTAL <= WINDOW:
            # Full attention within window
            o_from_cache = full_causal_attention(
                q_rope_decode,  # (1, NH, HD) — only the decode token
                kv_all_dequant,  # (N_TOTAL, HD) — all cached KV
                SCALE,
            )
        else:
            o_from_cache = swa_decode_attention(
                q_rope_decode, kv_all_dequant, decode_pos, SCALE, WINDOW,
            )
        
        # ════════════════════════════════════════════════════════════════
        # STEP 4: BF16 REFERENCE — process ALL tokens at once
        # ════════════════════════════════════════════════════════════════
        all_ids = token_ids[:N_TOTAL]
        all_pos = torch.arange(N_TOTAL, dtype=torch.int64, device=DEV)
        
        hidden_all = emb[all_ids]
        normed_all = rms(hidden_all, anorm, EPS)
        
        qa_all = r_qa.run(normed_all)
        kv_all = r_kv.run(normed_all)
        qa_n_all = rms(qa_all, qn, EPS)
        kv_n_all = rms(kv_all, kvn, EPS)
        q_all = r_qb.run(qa_n_all).view(N_TOTAL, NH, HD)
        q_rope_all = apply_gptj_rope(q_all, all_pos, cos_sin, NOPE, ROPE)
        kv_rope_all = apply_gptj_rope(kv_n_all.unsqueeze(1), all_pos, cos_sin, NOPE, ROPE).squeeze(1)
        
        # Full BF16 attention on all tokens
        o_ref_all = full_causal_attention(q_rope_all, kv_rope_all, SCALE)
        o_ref_decode = o_ref_all[N_PREFILL:]  # Only the decode token's output
        
        # ════════════════════════════════════════════════════════════════
        # COMPARE: cached KV decode vs BF16 reference decode
        # ════════════════════════════════════════════════════════════════
        c = F.cosine_similarity(o_from_cache.flatten().unsqueeze(0).float(), o_ref_decode.flatten().unsqueeze(0).float()).item()
        print(f"\n  Decode attention (cached KV) vs BF16 reference cosine: {c:.6f} {'✅' if c>=0.98 else '❌'}")
        print(f"  Cached output amax: {o_from_cache.amax():.4f}  BF16 ref amax: {o_ref_decode.amax():.4f}")
        print(f"  Cached output NaN: {torch.isnan(o_from_cache).any()}  BF16 NaN: {torch.isnan(o_ref_decode).any()}")
        
        # ════════════════════════════════════════════════════════════════
        # STEP 5: Full output pipeline — inverse RoPE + o_a BMM + o_b
        # ════════════════════════════════════════════════════════════════
        # Using cached attention output
        o_inv = apply_inv_gptj_rope(o_from_cache, decode_pos, cos_sin, NOPE, ROPE)
        o_grouped = o_inv.view(N_DECODE, OG, HPG * HD).permute(1, 0, 2)
        woa_3d = woa.view(OG, OL, HPG * HD)
        z_cached = torch.bmm(o_grouped, woa_3d.transpose(1, 2)).permute(1, 0, 2).reshape(N_DECODE, OG * OL)
        attn_out_cached = r_wob.run(z_cached)
        
        # Using BF16 reference
        o_inv_ref = apply_inv_gptj_rope(o_ref_decode, decode_pos, cos_sin, NOPE, ROPE)
        o_grouped_ref = o_inv_ref.view(N_DECODE, OG, HPG * HD).permute(1, 0, 2)
        z_ref = torch.bmm(o_grouped_ref, woa_3d.transpose(1, 2)).permute(1, 0, 2).reshape(N_DECODE, OG * OL)
        attn_out_ref = r_wob.run(z_ref)
        
        c_full = F.cosine_similarity(attn_out_cached.flatten().unsqueeze(0).float(), attn_out_ref.flatten().unsqueeze(0).float()).item()
        print(f"  Full output (cached) vs BF16 reference cosine: {c_full:.6f} {'✅' if c_full>=0.98 else '❌'}")
        
        # ════════════════════════════════════════════════════════════════
        # BUG REPRODUCTION: What vLLM currently does (uses raw kv, not cache)
        # ════════════════════════════════════════════════════════════════
        print(f"\n  --- BUG REPRODUCTION: vLLM Blackwell path ---")
        # vLLM's _attention_impl_blackwell calls full_sdpa_attention(q, kv, scale)
        # where kv is the RAW projection output (not from cache)
        # For decode, this only has 1 token of KV — missing all the prior tokens!
        o_buggy = full_causal_attention(q_rope_decode, kv_n_decode, SCALE)
        c_bug = F.cosine_similarity(o_buggy.flatten().unsqueeze(0).float(), o_ref_decode.flatten().unsqueeze(0).float()).item()
        print(f"  Buggy (raw kv, no cache) cosine: {c_bug:.6f} ❌ (should be low — missing context)")
        print(f"  This is why vLLM produces garbage: decode only has 1 KV vector,")
        print(f"  but needs to attend to ALL prior tokens' KV from the cache.")
    
    # Cleanup
    del r_qa, r_qb, r_kv, r_wob
    torch.cuda.empty_cache()
    return c, c_full


def main():
    print("=" * 70)
    print("  DeepSeek-V4 Decode Attention Pipeline Test")
    print("  Reproduces the vLLM Blackwell bug: KV cache not used for decode")
    print("=" * 70)
    
    # Test SWA layer (layer 60, compress_ratio=0)
    c_swa, c_swa_full = test_prefill_decode(60, 0)
    
    # Test C128A layer (layer 0, compress_ratio=128) — for this test, 
    # we just do full attention (not compressed) since compression
    # requires the compressor/indexer which is a separate concern
    # c_c128, c_c128_full = test_prefill_decode(0, 128)
    
    print(f"\n{'='*70}")
    print(f"  SUMMARY")
    print(f"  Layer 60 (SWA): decode attention cosine = {c_swa:.6f}, full output = {c_swa_full:.6f}")
    print(f"{'='*70}")
    print(f"\n  KEY TAKEAWAY: The KV cache write/read + attention pipeline")
    print(f"  must work for decode. Once verified, we can build the vLLM")
    print(f"  attention backend that uses this pipeline.")


if __name__ == "__main__":
    main()