Optimize gemm v7 output pipeline

mace/kernels/gemm.cc

@@ -471,7 +471,7 @@ inline void GemmTile(const float *A,
         // TODO(liyin): asm v7 prefetch and load optimization
         while (nw--) {
           float32x4_t b0, b1, b2, b3;
-          float32x4_t c0;
+          float32x4_t c0, c1, c2, c3;
 
           c0 = vld1q_f32(c_ptr0);
 
@@ -480,36 +480,37 @@ inline void GemmTile(const float *A,
           b2 = vld1q_f32(b_ptr2);
           b3 = vld1q_f32(b_ptr3);
 
+          c1 = vld1q_f32(c_ptr1);
+          c2 = vld1q_f32(c_ptr2);
+          c3 = vld1q_f32(c_ptr3);
+
           c0 = vmlaq_lane_f32(c0, b0, a00, 0);
           c0 = vmlaq_lane_f32(c0, b1, a00, 1);
           c0 = vmlaq_lane_f32(c0, b2, a01, 0);
           c0 = vmlaq_lane_f32(c0, b3, a01, 1);
 
           vst1q_f32(c_ptr0, c0);
-          c0 = vld1q_f32(c_ptr1);
 
-          c0 = vmlaq_lane_f32(c0, b0, a10, 0);
-          c0 = vmlaq_lane_f32(c0, b1, a10, 1);
-          c0 = vmlaq_lane_f32(c0, b2, a11, 0);
-          c0 = vmlaq_lane_f32(c0, b3, a11, 1);
+          c1 = vmlaq_lane_f32(c1, b0, a10, 0);
+          c1 = vmlaq_lane_f32(c1, b1, a10, 1);
+          c1 = vmlaq_lane_f32(c1, b2, a11, 0);
+          c1 = vmlaq_lane_f32(c1, b3, a11, 1);
 
-          vst1q_f32(c_ptr1, c0);
-          c0 = vld1q_f32(c_ptr2);
+          vst1q_f32(c_ptr1, c1);
 
-          c0 = vmlaq_lane_f32(c0, b0, a20, 0);
-          c0 = vmlaq_lane_f32(c0, b1, a20, 1);
-          c0 = vmlaq_lane_f32(c0, b2, a21, 0);
-          c0 = vmlaq_lane_f32(c0, b3, a21, 1);
+          c2 = vmlaq_lane_f32(c2, b0, a20, 0);
+          c2 = vmlaq_lane_f32(c2, b1, a20, 1);
+          c2 = vmlaq_lane_f32(c2, b2, a21, 0);
+          c2 = vmlaq_lane_f32(c2, b3, a21, 1);
 
-          vst1q_f32(c_ptr2, c0);
-          c0 = vld1q_f32(c_ptr3);
+          vst1q_f32(c_ptr2, c2);
 
-          c0 = vmlaq_lane_f32(c0, b0, a30, 0);
-          c0 = vmlaq_lane_f32(c0, b1, a30, 1);
-          c0 = vmlaq_lane_f32(c0, b2, a31, 0);
-          c0 = vmlaq_lane_f32(c0, b3, a31, 1);
+          c3 = vmlaq_lane_f32(c3, b0, a30, 0);
+          c3 = vmlaq_lane_f32(c3, b1, a30, 1);
+          c3 = vmlaq_lane_f32(c3, b2, a31, 0);
+          c3 = vmlaq_lane_f32(c3, b3, a31, 1);
 
-          vst1q_f32(c_ptr3, c0);
+          vst1q_f32(c_ptr3, c3);
 
           b_ptr0 += 4;
           b_ptr1 += 4;
@@ -586,7 +587,9 @@ void Gemm(const float *A,
   // It is better to use large block size if it fits for fast cache.
   // Assume l1 cache size is 32k, we load three blocks at a time (A, B, C),
   // the block size should be sqrt(32k / sizeof(T) / 3).
-  const index_t block_size = 48;
+  // As number of input channels of convolution is normally power of 2, and
+  // we have not optimized tiling remains, we use the following magic number
+  const index_t block_size = 64;
   const index_t block_tile_height = RoundUpDiv(height, block_size);
   const index_t block_tile_width = RoundUpDiv(width, block_size);
   const index_t block_tile_k = RoundUpDiv(K, block_size);