perf(decode): default gate/up to 1-row mmvq2_qwen + rmsnorm load elimination (sm_120)

kernels/csrc/cuda/fused/rmsnorm.cu

@@ -204,11 +204,15 @@ __global__ void add_rmsnorm2_q8_kernel(const __nv_bfloat16* __restrict__ x,
     __syncthreads();
     const float inv_rms = s_warp[0];
 
-    // Re-read the bf16-rounded residual sum (exactly as add_rmsnorm2_kernel does), so out_norm
-    // is bit-identical to the unfused path; then derive Q8_1 from the bf16-rounded out_norm.
+    // The bf16-rounded residual sum is already in registers (sv, just stored to out_sum):
+    // round it in-place instead of reloading osum4[t]. bf16(sv) is bit-identical to the
+    // store+reload rn_pack8/rn_unpack8 round-trip, so out_norm/Q8_1 stay bit-identical to
+    // the unfused path — but the dependent global load (right after the store, on this
+    // single-block latency-bound kernel) is removed from the critical path.
     const uint4* w4 = reinterpret_cast<const uint4*>(weight);
-    const uint4* osum4r = reinterpret_cast<const uint4*>(out_sum);
-    float svb[8], wv[8]; rn_unpack8(__ldg(osum4r + t), svb); rn_unpack8(__ldg(w4 + t), wv);
+    float svb[8], wv[8]; rn_unpack8(__ldg(w4 + t), wv);
+    #pragma unroll
+    for (int j = 0; j < 8; j++) svb[j] = __bfloat162float(__float2bfloat16(sv[j]));
     float ov[8], bv[8];
     #pragma unroll
     for (int j = 0; j < 8; j++) { ov[j] = svb[j] * inv_rms * wv[j]; bv[j] = __bfloat162float(__float2bfloat16(ov[j])); }

kernels/csrc/cuda/moe/expert_ffn_q4k.cu

@@ -855,8 +855,12 @@ void launch_moe_expert_ffn_q4k(
     if (gu2 < 0) { const char* g2 = getenv("SPARKINFER_GU2"); gu2 = (g2 && g2[0] == '0') ? 0 : 1; }
     static int gu_spec = -1;
     if (gu_spec < 0) { const char* gs = getenv("SPARKINFER_GU_SPEC"); gu_spec = (gs && gs[0] == '0') ? 0 : 1; }
+    // gate/up row-packing (2 rows/block, 8 warps). Default OFF: on RTX 5090 (sm_120) the
+    // 1-row-per-block gate_up_mmvq2_qwen_kernel is measurably faster than the packed variant
+    // — same 4 warps/row and identical math, but a smaller reduction footprint (sg/su[3][32]
+    // vs sg/su[2][3][32]) and no group indexing. Set SPARKINFER_GU_PACK2=1 to re-enable packing.
     static int gu_pack2 = -1;
-    if (gu_pack2 < 0) { const char* gp = getenv("SPARKINFER_GU_PACK2"); gu_pack2 = (gp && gp[0] == '0') ? 0 : 1; }
+    if (gu_pack2 < 0) { const char* gp = getenv("SPARKINFER_GU_PACK2"); gu_pack2 = (gp && gp[0] == '1') ? 1 : 0; }
     dim3 gu(num_tokens * top_k, (ffn + WPB - 1) / WPB);
     if (mmvq && gu2 && gate_type == 12 && up_type == 12) {   // faithful 4-warp mmvq gate/up
         const si_block_q8_1* q;