diff --git a/core/src/index/thirdparty/faiss/utils/distances.cpp b/core/src/index/thirdparty/faiss/utils/distances.cpp
index db7c222b2c..e97e873614 100644
--- a/core/src/index/thirdparty/faiss/utils/distances.cpp
+++ b/core/src/index/thirdparty/faiss/utils/distances.cpp
@@ -148,7 +148,7 @@ static void knn_inner_product_sse (const float * x,
     size_t k = res->k;
     size_t thread_max_num = omp_get_max_threads();
 
-    if (ny > parallel_policy_threshold) {
+    if (ny > parallel_policy_threshold || (nx < thread_max_num / 2 && ny >= thread_max_num * 32)) {
         size_t block_x = std::min(
                 get_L3_Size() / (d * sizeof(float) + thread_max_num * k * (sizeof(float) + sizeof(int64_t))),
                 nx);
@@ -173,24 +173,24 @@ static void knn_inner_product_sse (const float * x,
                 if(!bitset || !bitset->test(j)) {
                     size_t thread_no = omp_get_thread_num();
                     const float *y_j = y + j * d;
-                    for (size_t i = x_from; i < x_to; i++) {
-                        const float *x_i = x + i * d;
+                    const float *x_i = x + x_from * d;
+                    for (size_t i = 0; i < size; i++) {
                         float disij = fvec_inner_product (x_i, y_j, d);
-
-                        float * val_ = value + thread_no * thread_heap_size + (i - x_from) * k;
-                        int64_t * ids_ = labels + thread_no * thread_heap_size + (i - x_from) * k;
+                        float * val_ = value + thread_no * thread_heap_size + i * k;
+                        int64_t * ids_ = labels + thread_no * thread_heap_size + i * k;
                         if (disij > val_[0]) {
                             minheap_swap_top (k, val_, ids_, disij, j);
                         }
+                        x_i += d;
                     }
                 }
             }
 
+            // merge heap
             for (size_t t = 1; t < thread_max_num; t++) {
-                // merge heap
-                for (size_t i = x_from; i < x_to; i++) {
-                    float * __restrict value_x = value + (i - x_from) * k;
-                    int64_t * __restrict labels_x = labels + (i - x_from) * k;
+                for (size_t i = 0; i < size; i++) {
+                    float * __restrict value_x = value + i * k;
+                    int64_t * __restrict labels_x = labels + i * k;
                     float *value_x_t = value_x + t * thread_heap_size;
                     int64_t *labels_x_t = labels_x + t * thread_heap_size;
                     for (size_t j = 0; j < k; j++) {
@@ -201,14 +201,16 @@ static void knn_inner_product_sse (const float * x,
                 }
             }
 
-            for (size_t i = x_from; i < x_to; i++) {
-                float * value_x = value + (i - x_from) * k;
-                int64_t * labels_x = labels + (i - x_from) * k;
+            // sort
+            for (size_t i = 0; i < size; i++) {
+                float * value_x = value + i * k;
+                int64_t * labels_x = labels + i * k;
                 minheap_reorder (k, value_x, labels_x);
             }
 
-            memcpy(res->val+ x_from * k, value, thread_heap_size * sizeof(float));
-            memcpy(res->ids+ x_from * k, labels, thread_heap_size * sizeof(int64_t));
+            // copy result
+            memcpy(res->val + x_from * k, value, thread_heap_size * sizeof(float));
+            memcpy(res->ids + x_from * k, labels, thread_heap_size * sizeof(int64_t));
         }
         delete[] value;
         delete[] labels;
@@ -255,7 +257,7 @@ static void knn_L2sqr_sse (
     size_t k = res->k;
     size_t thread_max_num = omp_get_max_threads();
 
-    if (ny > parallel_policy_threshold) {
+    if (ny > parallel_policy_threshold || (nx < thread_max_num / 2 && ny >= thread_max_num * 32)) {
         size_t block_x = std::min(
                 get_L3_Size() / (d * sizeof(float) + thread_max_num * k * (sizeof(float) + sizeof(int64_t))),
                 nx);
@@ -280,24 +282,24 @@ static void knn_L2sqr_sse (
                 if(!bitset || !bitset->test(j)) {
                     size_t thread_no = omp_get_thread_num();
                     const float *y_j = y + j * d;
-                    for (size_t i = x_from; i < x_to; i++) {
-                        const float *x_i = x + i * d;
+                    const float *x_i = x + x_from * d;
+                    for (size_t i = 0; i < size; i++) {
                         float disij = fvec_L2sqr (x_i, y_j, d);
-
-                        float * val_ = value + thread_no * thread_heap_size + (i - x_from) * k;
-                        int64_t * ids_ = labels + thread_no * thread_heap_size + (i - x_from) * k;
+                        float * val_ = value + thread_no * thread_heap_size + i * k;
+                        int64_t * ids_ = labels + thread_no * thread_heap_size + i * k;
                         if (disij < val_[0]) {
                             maxheap_swap_top (k, val_, ids_, disij, j);
                         }
+                        x_i += d;
                     }
                 }
             }
 
+            // merge heap
             for (size_t t = 1; t < thread_max_num; t++) {
-                // merge heap
-                for (size_t i = x_from; i < x_to; i++) {
-                    float * __restrict value_x = value + (i - x_from) * k;
-                    int64_t * __restrict labels_x = labels + (i - x_from) * k;
+                for (size_t i = 0; i < size; i++) {
+                    float * __restrict value_x = value + i * k;
+                    int64_t * __restrict labels_x = labels + i * k;
                     float *value_x_t = value_x + t * thread_heap_size;
                     int64_t *labels_x_t = labels_x + t * thread_heap_size;
                     for (size_t j = 0; j < k; j++) {
@@ -308,19 +310,20 @@ static void knn_L2sqr_sse (
                 }
             }
 
-            for (size_t i = x_from; i < x_to; i++) {
-                float * value_x = value + (i - x_from) * k;
-                int64_t * labels_x = labels + (i - x_from) * k;
+            // sort
+            for (size_t i = 0; i < size; i++) {
+                float * value_x = value + i * k;
+                int64_t * labels_x = labels + i * k;
                 maxheap_reorder (k, value_x, labels_x);
             }
 
-            memcpy(res->val+ x_from * k, value, thread_heap_size * sizeof(float));
-            memcpy(res->ids+ x_from * k, labels, thread_heap_size * sizeof(int64_t));
+            // copy result
+            memcpy(res->val + x_from * k, value, thread_heap_size * sizeof(float));
+            memcpy(res->ids + x_from * k, labels, thread_heap_size * sizeof(int64_t));
         }
         delete[] value;
         delete[] labels;
 
-
     } else {
 
         float * value = res->val;