x64: brgemm: avx: bd_block should not be smaller than vpad

Author: ankalinin

src/cpu/x64/brgemm/brgemm_utils.cpp

@@ -240,20 +240,27 @@ status_t brgemm_blocking(brgemm_desc_t *brg) {
         brg->ldb = brg->load_dim / brg->ld_block;
         brg->ldb_tail = brg->load_dim % brg->ld_block;
 
+        const int max_vpad = nstl::max(
+                brg->brgattr.max_top_vpad, brg->brgattr.max_bottom_vpad);
+
         int adj_ld_block2 = calculate_ldb_params(brg, 4);
         int max_bcast_block = calculate_max_bcast_block(brg, adj_ld_block2);
-
         // reduce 'ld_block2' to allow a larger 'bd_block'
-        const int max_vpad = nstl::max(
-                brg->brgattr.max_top_vpad, brg->brgattr.max_bottom_vpad);
         if (is_superset(brg->isa_impl, avx2) && max_bcast_block < max_vpad) {
-            adj_ld_block2 = calculate_ldb_params(brg, 2);
-            max_bcast_block = calculate_max_bcast_block(brg, adj_ld_block2);
+            for (int try_ld_block2 = 2; try_ld_block2 > 0; --try_ld_block2) {
+                adj_ld_block2 = calculate_ldb_params(brg, try_ld_block2);
+                max_bcast_block = calculate_max_bcast_block(brg, adj_ld_block2);
+                if (max_bcast_block >= max_vpad) break;
+            }
+            // bcast block in brgemm kernel should be greater than virtual
+            // padding to avoid possible functional issues
+            if (max_bcast_block < max_vpad) return status::unimplemented;
         }
 
-        const int min_block = 1;
+        const int min_block = nstl::max(1, max_vpad);
+
         float best_bd_block_eff = 0.f;
-        brg->bd_block = 1;
+        brg->bd_block = max_bcast_block;
         for (int bd_block = max_bcast_block; bd_block >= min_block;
                 bd_block--) {
             const auto bd_block_disb = static_cast<float>(brg->bcast_dim)