CUDA/HIP: ssm-scan: switch from shared memory to reisters, fixes indexing problem on warp64 devices

Author: IMbackK

ggml/src/ggml-cuda/ssm-scan.cu

@@ -9,19 +9,9 @@ __global__ void __launch_bounds__(splitD, 2)
                  const int src2_nb1, const int src2_nb2, const int src3_nb1,
                  const int src4_nb2, const int src4_nb3, const int src5_nb2, const int src5_nb3,
                  const int64_t s_off, const int64_t d_inner, const int64_t L) {
-
-    constexpr int warp_size = ggml_cuda_get_physical_warp_size();
     const int bidx = blockIdx.x;  // split along B (sequences)
     const int bidy = blockIdx.y;  // split along D (d_inner)
     const int tid  = threadIdx.x;
-    const int wid  = tid / 32;
-    const int wtid = tid % 32;
-
-    extern __shared__ float smem[];
-    const int               stride_sA  = N + 1;
-    const int               stride_ss0 = N + 1;
-    float *                 smem_A     = smem;
-    float *                 smem_s0    = smem_A + splitD * stride_sA;
 
     const float * s0_block = (const float *) ((const char *) src0 + src6[bidx] * src0_nb3 + bidy * splitD * src0_nb2);
     const float * x_block  = (const float *) ((const char *) src1 + (bidx * src1_nb3) + bidy * splitD * sizeof(float));
@@ -41,46 +31,35 @@ __global__ void __launch_bounds__(splitD, 2)
     const int stride_s  = stride_s0;
     const int stride_y  = d_inner;
 
-    // can N not be 16? for example 32?
-    if (N == 16) {
-#pragma unroll
-        for (size_t i = 0; i < splitD / 4; i += 2) {
-            float value = A_block[(wid * warp_size + i) * stride_A + wtid];
-            // todo: bank conflict
-            // I am always confused with how to use the swizzling method to solve
-            // bank conflit. Hoping somebody can tell me.
-            smem_A[(wid * warp_size + i) * stride_sA + wtid + ((wtid / 16) > 0 ? 1 : 0)] = value;
-        }
+    float A[N];
+    float s[N];
+
 #pragma unroll
-        for (size_t i = 0; i < splitD / 4; i += 2) {
-            float value = s0_block[(wid * warp_size + i) * stride_s0 + wtid];
-            smem_s0[(wid * warp_size + i) * stride_ss0 + wtid + ((wtid / 16) > 0 ? 1 : 0)] = value;
-        }
+    for (int j = 0; j < N; j++) {
+        A[j] = A_block[tid * N + j];
+        s[j] = s0_block[tid * stride_s0 + j];
     }
 
-    __syncthreads();
-
     for (int64_t i = 0; i < L; i++) {
         float dt_soft_plus = dt_block[i * stride_dt + tid];
-        if (dt_soft_plus <= 20.0f) {
-            dt_soft_plus = log1pf(exp(dt_soft_plus));
-        }
-        float x_dt = x_block[i * stride_x + tid] * dt_soft_plus;
+        dt_soft_plus = (dt_soft_plus > 20.0f) ? dt_soft_plus : log1pf(expf(dt_soft_plus));
+
+        const float x_dt = x_block[i * stride_x + tid] * dt_soft_plus;
         float sumf = 0.0f;
+
 #pragma unroll
         for (size_t j = 0; j < N; j++) {
-            float state = (smem_s0[tid * stride_ss0 + j] * expf(dt_soft_plus * smem_A[tid * stride_sA + j])) +
-                          (B_block[i * stride_B + j] * x_dt);
-            sumf += state * C_block[i * stride_C + j];
-            if (i == L - 1) {
-                s_block[tid * stride_s + j] = state;
-            } else {
-                smem_s0[tid * stride_ss0 + j] = state;
-            }
+            const float exp_term = expf(dt_soft_plus * A[j]);
+            s[j] = fmaf(s[j], exp_term, B_block[i * stride_B + j] * x_dt);
+            sumf = fmaf(s[j], C_block[i * stride_C + j], sumf);
         }
-        __syncthreads();
         y_block[i * stride_y + tid] = sumf;
     }
+
+#pragma unroll
+    for (int j = 0; j < N; j++) {
+        s_block[tid * stride_s + j] = s[j];
+    }
 }
 
 // assumes as many threads as d_state