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IQ.Pilot Release Commit @ 0798119
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IQ.Lvbs history cleanup
205
tinygrad_repo/extra/gemm/amd_flash_attention.py
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205
tinygrad_repo/extra/gemm/amd_flash_attention.py
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from tinygrad import Tensor, UOp, getenv
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from tinygrad.uop.ops import AxisType, KernelInfo, Ops
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from tinygrad.dtype import AddrSpace, dtypes
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from tinygrad.helpers import DEBUG, GlobalCounters, Context
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import math
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BLOCK_M, BLOCK_N = 64, 64
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WARP_SIZE = 32
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WMMA_M, WMMA_N, WMMA_K = 16, 16, 16
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WAVES_M, WAVES_N = 4, 1
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LANES_PER_WAVE_M, LANES_PER_WAVE_N = 2, 16
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WMMA_ACC = WMMA_M // LANES_PER_WAVE_M
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THREADS_PER_BLOCK = WARP_SIZE * WAVES_M * WAVES_N
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LDS_PAD = 4 # pad LDS rows to reduce bank conflicts
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WMMA_ARG = ((WMMA_M, WMMA_N, WMMA_K), 'AMD', 32)
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LOG2E = math.log2(math.e)
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def warp_shfl_xor(val, offset, lane):
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"""Read val from lane ^ offset using ds_bpermute."""
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idx = ((lane ^ offset) * 4).cast(dtypes.int)
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return UOp(Ops.CUSTOM, dtypes.float, (idx, val),
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arg="__builtin_bit_cast(float, __builtin_amdgcn_ds_bpermute({0}, __builtin_bit_cast(int, {1})))")
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def warp_reduce_max(val, lane):
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"""Tree reduce MAX across LANES_PER_WAVE_N=16 lanes."""
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for offset in [8, 4, 2, 1]:
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val = UOp(Ops.MAX, dtypes.float, (val, warp_shfl_xor(val, offset, lane)))
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return val
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def warp_reduce_sum(val, lane):
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"""Tree reduce SUM across LANES_PER_WAVE_N=16 lanes."""
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for offset in [8, 4, 2, 1]:
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val = val + warp_shfl_xor(val, offset, lane)
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return val
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def amd_flash_attention(o:UOp, q:UOp, k:UOp, v:UOp) -> UOp:
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# inputs are (B*H, N, D)
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BH, N, D = q.shape
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assert N % BLOCK_M == 0 and N % BLOCK_N == 0, f"N={N} must be divisible by BLOCK_M={BLOCK_M} and BLOCK_N={BLOCK_N}"
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assert D % WMMA_K == 0 and D % LANES_PER_WAVE_N == 0, f"D={D} must be divisible by WMMA_K={WMMA_K} and LANES_PER_WAVE_N={LANES_PER_WAVE_N}"
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assert BLOCK_M % (WAVES_M * WMMA_M) == 0 and BLOCK_N % LANES_PER_WAVE_N == 0
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TM = BLOCK_M // (WAVES_M * LANES_PER_WAVE_M)
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TN = BLOCK_N // (WAVES_N * LANES_PER_WAVE_N)
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TD = D // (WAVES_N * LANES_PER_WAVE_N)
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SCALE = 1.0 / math.sqrt(D)
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block_bh = UOp.range(BH, 0, AxisType.GLOBAL)
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block_m = UOp.range(N // BLOCK_M, 1, AxisType.GLOBAL)
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q = q.reshape(BH, N//BLOCK_M, BLOCK_M, D)[block_bh, block_m]
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k = k.reshape(BH, N//BLOCK_N, BLOCK_N, D)[block_bh]
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v = v.reshape(BH, N//BLOCK_N, BLOCK_N, D)[block_bh]
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o = o.reshape(BH, N//BLOCK_M, BLOCK_M, D)[block_bh, block_m]
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wave_m = UOp.range(WAVES_M, 2, AxisType.LOCAL)
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wave_n = UOp.range(WAVES_N, 3, AxisType.LOCAL)
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lane = UOp.range(WARP_SIZE, -1, AxisType.WARP)
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tid = (wave_m * WAVES_N + wave_n) * WARP_SIZE + lane
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lane_m = lane // LANES_PER_WAVE_N
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lane_n = lane % LANES_PER_WAVE_N
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# LDS allocation: slot 0 = Q then P (shared), slot 1 = K then V
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# TODO: the memory planner should be able to find this reuse
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ELEMS_PER_THREAD = BLOCK_M * D // THREADS_PER_BLOCK
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QP_lds = UOp.placeholder((BLOCK_M, D + LDS_PAD), dtypes.half, slot=0, addrspace=AddrSpace.LOCAL)
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KV_lds = UOp.placeholder((BLOCK_N, D + LDS_PAD), dtypes.half, slot=1, addrspace=AddrSpace.LOCAL)[:, :D]
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# register state
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acc = UOp.placeholder((TM, TD), dtypes.float, slot=2, addrspace=AddrSpace.REG)
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m_i = UOp.placeholder((TM,), dtypes.float, slot=3, addrspace=AddrSpace.REG)
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l_i = UOp.placeholder((TM,), dtypes.float, slot=4, addrspace=AddrSpace.REG)
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acc = acc.after(acc.store(acc.const_like(0)))
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m_i = m_i.after(m_i.store(m_i.const_like(-math.inf)))
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l_i = l_i.after(l_i.store(l_i.const_like(0)))
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# ====== KV tile loop ======
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n_tile = UOp.range(N // BLOCK_N, 100, AxisType.REDUCE)
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# load Q + K into LDS (Q reloaded each iteration since P overwrites slot 0)
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Q_lds = QP_lds[:, :D]
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Q_store = Q_lds.after(n_tile).reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid].store(
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q.reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid])
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K_store = KV_lds.reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid].store(
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k[n_tile].reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid])
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qk_load_barrier = UOp.barrier(UOp.group(Q_store, K_store))
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Q_lds = Q_lds.after(qk_load_barrier)
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KV_lds_k = KV_lds.after(qk_load_barrier)
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# -- S = Q @ K^T via WMMA (re-init each n_tile) --
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S_reg = UOp.placeholder((TM, TN), dtypes.float, slot=6, addrspace=AddrSpace.REG)
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S_reg = S_reg.after(S_reg.after(n_tile).store(S_reg.const_like(0)))
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k_qk = UOp.range(D // WMMA_K, 101, AxisType.REDUCE)
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tm1 = UOp.range(TM // WMMA_ACC, 200, AxisType.LOOP)
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tn1 = UOp.range(TN, 201, AxisType.LOOP)
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S_frag = S_reg.reshape(TM // WMMA_ACC, WMMA_ACC, TN).permute(0, 2, 1)[tm1, tn1]
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q_frag = Q_lds.reshape(WAVES_M, TM // WMMA_ACC, WMMA_M, D // WMMA_K, WMMA_K)[wave_m, tm1, lane_n, k_qk]
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k_frag = KV_lds_k.reshape(WAVES_N, TN, WMMA_N, D // WMMA_K, WMMA_K)[wave_n, tn1, lane_n, k_qk]
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qk = UOp(Ops.SHAPED_WMMA, dtypes.float, (q_frag, k_frag, S_frag.after(k_qk)), arg=WMMA_ARG)
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qk_done = S_frag.store(qk).end(tm1, tn1).end(k_qk)
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S_reg = S_reg.after(qk_done)
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# -- softmax in registers with warp shuffles --
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S_reg = S_reg.after(S_reg.store(S_reg * SCALE))
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# per-thread local row max over TN=4 elements, then warp reduce across 16 lanes
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m_ij = UOp.placeholder((TM,), dtypes.float, slot=7, addrspace=AddrSpace.REG)
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m_ij = m_ij.after(m_ij.after(n_tile).store(m_ij.const_like(-math.inf)))
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rm2 = UOp.range(TN, 261, AxisType.REDUCE)
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m_ij = m_ij.after(m_ij.store(m_ij.after(rm2).maximum(S_reg[:, rm2])).end(rm2))
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# warp reduce max (in-place)
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ri_w = UOp.range(TM, 270, AxisType.LOOP)
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m_ij = m_ij.after(m_ij[ri_w].store(warp_reduce_max(m_ij[ri_w], lane)).end(ri_w))
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# compute P = exp(S - m_ij) in S_reg
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S_reg = S_reg.after(S_reg.store(((S_reg - m_ij.reshape(TM, 1).expand(TM, TN)) * LOG2E).exp2()))
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p_local = UOp.placeholder((TM,), dtypes.float, slot=8, addrspace=AddrSpace.REG)
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p_local = p_local.after(p_local.after(n_tile).store(p_local.const_like(0)))
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rp2 = UOp.range(TN, 291, AxisType.REDUCE)
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p_local = p_local.after(p_local.store(p_local.after(rp2) + S_reg[:, rp2]).end(rp2))
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ri_ws = UOp.range(TM, 295, AxisType.LOOP)
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p_sum = p_local.after(p_local[ri_ws].store(warp_reduce_sum(p_local[ri_ws], lane)).end(ri_ws))
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# write P = exp(S - m_ij) to P_lds (reuses slot 0, Q no longer needed)
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P_lds = QP_lds[:, :BLOCK_N]
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P_write = P_lds.reshape(WAVES_M, TM // WMMA_ACC, WMMA_ACC, LANES_PER_WAVE_M, WAVES_N, TN, LANES_PER_WAVE_N)
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P_write = P_write.permute((0, 4, 3, 6, 1, 2, 5)).reshape(THREADS_PER_BLOCK, TM, TN)
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# TODO: P_write[tid].store(S_reg.cast(dtypes.half)) — shaped store fails due to RESHAPE(DEFINE_LOCAL) surviving linearization
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rw1 = UOp.range(TM, 296, AxisType.LOOP)
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rw2 = UOp.range(TN, 297, AxisType.LOOP)
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P_store = P_write[tid, rw1, rw2].store(S_reg[rw1, rw2].cast(dtypes.half)).end(rw1, rw2)
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# -- online softmax correction --
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ri4 = UOp.range(TM, 330, AxisType.LOOP)
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m_new_val = m_i[ri4].maximum(m_ij[ri4])
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alpha_val = ((m_i[ri4] - m_new_val) * LOG2E).exp2()
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beta_val = ((m_ij[ri4] - m_new_val) * LOG2E).exp2()
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rj4 = UOp.range(TD, 331, AxisType.LOOP)
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correction = UOp.group(
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acc[ri4, rj4].store(alpha_val * acc[ri4, rj4]).end(rj4),
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l_i[ri4].store(alpha_val * l_i[ri4] + beta_val * p_sum[ri4]),
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m_i[ri4].store(m_new_val),
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).end(ri4)
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acc = acc.after(correction)
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l_i = l_i.after(correction)
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m_i = m_i.after(correction)
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# load V into KV_lds (must wait for QK WMMA to finish reading K from KV_lds)
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V_store = KV_lds.after(qk_done).reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid].store(
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v[n_tile].reshape(THREADS_PER_BLOCK, ELEMS_PER_THREAD)[tid])
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pv_barrier = UOp.barrier(UOp.group(P_store, V_store))
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P_lds = P_lds.after(pv_barrier)
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KV_lds_v = KV_lds.after(pv_barrier)
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# -- acc += P @ V via WMMA --
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k_pv = UOp.range(BLOCK_N // WMMA_K, 400, AxisType.REDUCE)
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tm2 = UOp.range(TM // WMMA_ACC, 401, AxisType.LOOP)
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tn2 = UOp.range(TD, 402, AxisType.LOOP)
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acc_frag = acc.reshape(TM // WMMA_ACC, WMMA_ACC, TD).permute(0, 2, 1)[tm2, tn2]
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p_frag = P_lds.reshape(WAVES_M, TM // WMMA_ACC, WMMA_M, BLOCK_N // WMMA_K, WMMA_K)[wave_m, tm2, lane_n, k_pv]
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v_frag = KV_lds_v.reshape(WAVES_N, TD, WMMA_N, BLOCK_N // WMMA_K, WMMA_K)[wave_n, tn2, lane_n, k_pv]
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pv = UOp(Ops.SHAPED_WMMA, dtypes.float, (p_frag, v_frag, acc_frag.after(k_pv)), arg=WMMA_ARG)
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# end KV tile loop
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n_tile_end = acc_frag.store(pv).end(tm2, tn2).end(k_pv).barrier().end(n_tile)
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acc = acc.after(n_tile_end)
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l_i = l_i.after(n_tile_end)
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m_i = m_i.after(n_tile_end)
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# normalize: acc /= l_i
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acc = acc.after(acc.store(acc * (1 / l_i).reshape(TM, 1).expand(TM, TD)))
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# store output
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o = o.reshape(WAVES_M, TM // WMMA_ACC, WMMA_ACC, LANES_PER_WAVE_M, WAVES_N, TD, LANES_PER_WAVE_N)
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o = o.permute((0, 4, 3, 6, 1, 2, 5)).reshape(THREADS_PER_BLOCK, TM, TD)
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return o[tid].store(acc).end(wave_m, wave_n, lane).end(block_m, block_bh).sink(arg=KernelInfo(opts_to_apply=()))
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if __name__ == "__main__":
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B, H, N, D = getenv("B", 1), getenv("H", 32), getenv("N", 1024), getenv("D", 64)
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q = Tensor.rand(B, H, N, D).cast(dtypes.half)
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k = Tensor.rand(B, H, N, D).cast(dtypes.half)
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v = Tensor.rand(B, H, N, D).cast(dtypes.half)
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o = Tensor.empty(B, H, N, D, dtype=dtypes.float)
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with Context(DEBUG=0): Tensor.realize(q, k, v)
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q_flat, k_flat, v_flat, o_flat = q.reshape(B*H, N, D), k.reshape(B*H, N, D), v.reshape(B*H, N, D), o.reshape(B*H, N, D)
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NUM_RUNS = getenv("CNT", 5)
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ets = []
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with Context(DEBUG=2):
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for _ in range(NUM_RUNS):
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GlobalCounters.reset()
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tst = Tensor.custom_kernel(o_flat, q_flat, k_flat, v_flat, fxn=amd_flash_attention)[0].realize()
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ets.append(GlobalCounters.time_sum_s)
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print(f"best time: {min(ets)*1e3:.2f}ms")
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if getenv("VERIFY", 1):
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with Context(DEBUG=0):
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ref = q.float().scaled_dot_product_attention(k.float(), v.float()).reshape(B*H, N, D).realize()
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err = (ref - tst).square().mean().item()
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print(f"mean squared error {err}")
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if err > 1e-2:
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raise RuntimeError("flash attention is wrong!")
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else:
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print("flash attention is correct!")
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