| """Llama-shaped decoder with INT4 group-quantised weights (W4A16), shipped pre-packed. |
| |
| Every 2-D weight arrives as a triple `(packed, scale, zero)`: |
| |
| packed : (out, in // 2) uint8 -- two 4-bit codes per byte, LOW nibble first |
| scale : (out, in // group) bf16 |
| zero : (out, in // group) uint8 (values 0..15) |
| |
| and its value is `(code - zero) * scale`, with `group` = `cfg["group"]` contiguous input elements |
| sharing one (scale, zero). This is the AWQ / GPTQ asymmetric layout. |
| |
| The weights are quantised ONCE, here, and the reference dequantises exactly these bytes. That is not a |
| convenience: if the fixture were fp32 and the agent had to quantise, a *correct* int4 kernel would |
| disagree with the reference by the quantisation error rather than by its own error -- measured at 10x |
| the tolerance for the fp8 case. |
| """ |
| from model import HELPERS_CORE |
|
|
| QUANT = r''' |
| |
| _INT4_GROUP = None # set by make_weights / build_model from cfg |
| |
| |
| def _quantise(w, dt, group=128): |
| """fp32 -> asymmetric int4 with per-group (scale, zero), packed two codes per byte.""" |
| if dt == "bf16": |
| return w.to(torch.bfloat16) |
| if dt != "int4": |
| raise ValueError(dt) |
| out, inn = w.shape |
| g = w.view(out, inn // group, group) |
| lo = g.amin(dim=-1, keepdim=True) |
| hi = g.amax(dim=-1, keepdim=True) |
| scale = ((hi - lo) / 15.0).clamp(min=1e-8) |
| zero = torch.round(-lo / scale).clamp(0, 15) |
| code = torch.round(g / scale + zero).clamp(0, 15).to(torch.uint8).view(out, inn) |
| packed = (code[:, 0::2] | (code[:, 1::2] << 4)).contiguous() |
| return (packed, scale.squeeze(-1).to(torch.bfloat16), zero.squeeze(-1).to(torch.uint8)) |
| |
| |
| def _deq(w, group=128): |
| """(packed, scale, zero) -> bf16. Plain bf16 weights pass through.""" |
| if not isinstance(w, tuple): |
| return w |
| packed, scale, zero = w |
| out = packed.shape[0] |
| lo = (packed & 0xF).to(torch.int16) |
| hi = (packed >> 4).to(torch.int16) |
| code = torch.stack([lo, hi], dim=-1).view(out, -1) # interleave back to (out, in) |
| inn = code.shape[1] |
| code = code.view(out, inn // group, group).float() |
| v = (code - zero.float().unsqueeze(-1)) * scale.float().unsqueeze(-1) |
| return v.view(out, inn).to(torch.bfloat16) |
| ''' |
|
|
| BODY = r''' |
| def make_weights(cfg, seed=0, device="cuda"): |
| """Deterministic 1/sqrt(fan_in)-scaled weights, shipped ALREADY int4-quantised.""" |
| g = torch.Generator(device=device).manual_seed(seed) |
| d, ffn, n_q, n_kv, hd = cfg["d"], cfg["ffn"], cfg["n_q"], cfg["n_kv"], cfg["hd"] |
| dt, grp = cfg["wdtype"], cfg["group"] |
| |
| def rnd(*shape, fan_in): |
| w = torch.randn(*shape, device=device, dtype=torch.float32, generator=g) / (fan_in ** 0.5) |
| return _quantise(w, dt, grp) |
| |
| ones = lambda: torch.ones(d, device=device, dtype=torch.bfloat16) |
| W = {"embed": rnd(cfg["vocab"], d, fan_in=d), "final_norm": ones(), "layers": []} |
| for _ in range(cfg["layers"]): |
| W["layers"].append(dict( |
| in_norm=ones(), post_norm=ones(), |
| q=rnd(n_q * hd, d, fan_in=d), k=rnd(n_kv * hd, d, fan_in=d), |
| v=rnd(n_kv * hd, d, fan_in=d), o=rnd(d, n_q * hd, fan_in=n_q * hd), |
| gate=rnd(ffn, d, fan_in=d), up=rnd(ffn, d, fan_in=d), down=rnd(d, ffn, fan_in=ffn))) |
| return W |
| |
| |
| def make_kv(cfg, batch, prefill_len, max_seq, seed=0, device="cuda"): |
| """KV cache already holding `prefill_len` tokens. Decode starts at pos = prefill_len.""" |
| g = torch.Generator(device=device).manual_seed(seed + 777) |
| kv = [] |
| for _ in range(cfg["layers"]): |
| k = torch.zeros(batch, cfg["n_kv"], max_seq, cfg["hd"], device=device, dtype=torch.bfloat16) |
| v = torch.zeros_like(k) |
| k[:, :, :prefill_len] = torch.randn(batch, cfg["n_kv"], prefill_len, cfg["hd"], device=device, |
| dtype=torch.float32, generator=g).to(torch.bfloat16) * 0.5 |
| v[:, :, :prefill_len] = torch.randn(batch, cfg["n_kv"], prefill_len, cfg["hd"], device=device, |
| dtype=torch.float32, generator=g).to(torch.bfloat16) * 0.5 |
| kv.append((k, v)) |
| return kv |
| |
| |
| def build_model(weights, kv_cache, cfg, max_seq_len): |
| """UNTIMED setup. Dequantises ONCE here rather than per step -- dequantising inside every step |
| allocates GBs per call, which perturbs the caching allocator enough that cuBLAS picks different |
| GEMV algorithms run-to-run and two bit-identical implementations drift apart.""" |
| cos, sin = _rope_cache(cfg, max_seq_len, weights["final_norm"].device) |
| grp = cfg["group"] |
| W = {"embed": _deq(weights["embed"], grp), "final_norm": weights["final_norm"], |
| "layers": [{k: (v if k.endswith("norm") else _deq(v, grp)) for k, v in L.items()} |
| for L in weights["layers"]]} |
| return {"W": W, "kv": kv_cache, "cfg": cfg, "cos": cos, "sin": sin} |
| |
| |
| @torch.no_grad() |
| def decode_step(handle, token_ids, pos): |
| """One decode step for every sequence in the batch. Appends this position's K/V into the cache. |
| |
| token_ids: (B,) int64 pos: int, the absolute position being written |
| returns: (B, vocab) logits |
| """ |
| W, kv, cfg = handle["W"], handle["kv"], handle["cfg"] |
| cos, sin = handle["cos"], handle["sin"] |
| B = token_ids.shape[0] |
| n_q, n_kv, hd = cfg["n_q"], cfg["n_kv"], cfg["hd"] |
| rep = n_q // n_kv |
| |
| x = W["embed"][token_ids] |
| for li, L in enumerate(W["layers"]): |
| h = _rms_norm(x, L["in_norm"], cfg["eps"]) |
| q = (h @ L["q"].T).view(B, n_q, 1, hd) |
| k = (h @ L["k"].T).view(B, n_kv, 1, hd) |
| v = (h @ L["v"].T).view(B, n_kv, 1, hd) |
| q = _apply_rope(q, cos, sin, pos) |
| k = _apply_rope(k, cos, sin, pos) |
| kc, vc = kv[li] |
| kc[:, :, pos:pos + 1] = k |
| vc[:, :, pos:pos + 1] = v |
| kk = kc[:, :, :pos + 1].repeat_interleave(rep, dim=1) |
| vv = vc[:, :, :pos + 1].repeat_interleave(rep, dim=1) |
| att = F.scaled_dot_product_attention(q, kk, vv) |
| x = x + (att.reshape(B, n_q * hd) @ L["o"].T) |
| h = _rms_norm(x, L["post_norm"], cfg["eps"]) |
| x = x + ((F.silu(h @ L["gate"].T) * (h @ L["up"].T)) @ L["down"].T) |
| x = _rms_norm(x, W["final_norm"], cfg["eps"]) |
| return x @ W["embed"].T # tied lm_head |
| ''' |
|
|
| MODEL_SRC = HELPERS_CORE + QUANT + BODY |
|
|
