net: openvswitch: optimize flow-mask looking up

The full looking up on flow table traverses all mask array.
If mask-array is too large, the number of invalid flow-mask
increase, performance will be drop.

One bad case, for example: M means flow-mask is valid and NULL
of flow-mask means deleted.

+-------------------------------------------+
| M | NULL | ...                  | NULL | M|
+-------------------------------------------+

In that case, without this patch, openvswitch will traverses all
mask array, because there will be one flow-mask in the tail. This
patch changes the way of flow-mask inserting and deleting, and the
mask array will be keep as below: there is not a NULL hole. In the
fast path, we can "break" "for" (not "continue") in flow_lookup
when we get a NULL flow-mask.

         "break"
            v
+-------------------------------------------+
| M | M |  NULL |...           | NULL | NULL|
+-------------------------------------------+

This patch don't optimize slow or control path, still using ma->max
to traverse. Slow path:
* tbl_mask_array_realloc
* ovs_flow_tbl_lookup_exact
* flow_mask_find

Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Tested-by: Greg Rose <gvrose8192@gmail.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/flow_table.c

@@ -518,8 +518,8 @@ static struct sw_flow *flow_lookup(struct flow_table *tbl,
 				   u32 *n_mask_hit,
 				   u32 *index)
 {
-	struct sw_flow_mask *mask;
 	struct sw_flow *flow;
+	struct sw_flow_mask *mask;
 	int i;
 
 	if (*index < ma->max) {
@@ -538,7 +538,7 @@ static struct sw_flow *flow_lookup(struct flow_table *tbl,
 
 		mask = rcu_dereference_ovsl(ma->masks[i]);
 		if (!mask)
-			continue;
+			break;
 
 		flow = masked_flow_lookup(ti, key, mask, n_mask_hit);
 		if (flow) { /* Found */
@@ -695,8 +695,7 @@ struct sw_flow *ovs_flow_tbl_lookup_ufid(struct flow_table *tbl,
 int ovs_flow_tbl_num_masks(const struct flow_table *table)
 {
 	struct mask_array *ma = rcu_dereference_ovsl(table->mask_array);
-
-	return ma->count;
+	return READ_ONCE(ma->count);
 }
 
 static struct table_instance *table_instance_expand(struct table_instance *ti,
@@ -705,21 +704,33 @@ static struct table_instance *table_instance_expand(struct table_instance *ti,
 	return table_instance_rehash(ti, ti->n_buckets * 2, ufid);
 }
 
-static void tbl_mask_array_delete_mask(struct mask_array *ma,
-				       struct sw_flow_mask *mask)
+static void tbl_mask_array_del_mask(struct flow_table *tbl,
+				    struct sw_flow_mask *mask)
 {
-	int i;
+	struct mask_array *ma = ovsl_dereference(tbl->mask_array);
+	int i, ma_count = READ_ONCE(ma->count);
 
 	/* Remove the deleted mask pointers from the array */
-	for (i = 0; i < ma->max; i++) {
-		if (mask == ovsl_dereference(ma->masks[i])) {
-			RCU_INIT_POINTER(ma->masks[i], NULL);
-			ma->count--;
-			kfree_rcu(mask, rcu);
-			return;
-		}
+	for (i = 0; i < ma_count; i++) {
+		if (mask == ovsl_dereference(ma->masks[i]))
+			goto found;
 	}
+
 	BUG();
+	return;
+
+found:
+	WRITE_ONCE(ma->count, ma_count -1);
+
+	rcu_assign_pointer(ma->masks[i], ma->masks[ma_count -1]);
+	RCU_INIT_POINTER(ma->masks[ma_count -1], NULL);
+
+	kfree_rcu(mask, rcu);
+
+	/* Shrink the mask array if necessary. */
+	if (ma->max >= (MASK_ARRAY_SIZE_MIN * 2) &&
+	    ma_count <= (ma->max / 3))
+		tbl_mask_array_realloc(tbl, ma->max / 2);
 }
 
 /* Remove 'mask' from the mask list, if it is not needed any more. */
@@ -733,17 +744,8 @@ static void flow_mask_remove(struct flow_table *tbl, struct sw_flow_mask *mask)
 		BUG_ON(!mask->ref_count);
 		mask->ref_count--;
 
-		if (!mask->ref_count) {
-			struct mask_array *ma;
-
-			ma = ovsl_dereference(tbl->mask_array);
-			tbl_mask_array_delete_mask(ma, mask);
-
-			/* Shrink the mask array if necessary. */
-			if (ma->max >= (MASK_ARRAY_SIZE_MIN * 2) &&
-			    ma->count <= (ma->max / 3))
-				tbl_mask_array_realloc(tbl, ma->max / 2);
-		}
+		if (!mask->ref_count)
+			tbl_mask_array_del_mask(tbl, mask);
 	}
 }
 
@@ -807,6 +809,29 @@ static struct sw_flow_mask *flow_mask_find(const struct flow_table *tbl,
 	return NULL;
 }
 
+static int tbl_mask_array_add_mask(struct flow_table *tbl,
+				   struct sw_flow_mask *new)
+{
+	struct mask_array *ma = ovsl_dereference(tbl->mask_array);
+	int err, ma_count = READ_ONCE(ma->count);
+
+	if (ma_count >= ma->max) {
+		err = tbl_mask_array_realloc(tbl, ma->max +
+					      MASK_ARRAY_SIZE_MIN);
+		if (err)
+			return err;
+
+		ma = ovsl_dereference(tbl->mask_array);
+	}
+
+	BUG_ON(ovsl_dereference(ma->masks[ma_count]));
+
+	rcu_assign_pointer(ma->masks[ma_count], new);
+	WRITE_ONCE(ma->count, ma_count +1);
+
+	return 0;
+}
+
 /* Add 'mask' into the mask list, if it is not already there. */
 static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
 			    const struct sw_flow_mask *new)
@@ -815,9 +840,6 @@ static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
 
 	mask = flow_mask_find(tbl, new);
 	if (!mask) {
-		struct mask_array *ma;
-		int i;
-
 		/* Allocate a new mask if none exsits. */
 		mask = mask_alloc();
 		if (!mask)
@@ -826,29 +848,9 @@ static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
 		mask->range = new->range;
 
 		/* Add mask to mask-list. */
-		ma = ovsl_dereference(tbl->mask_array);
-		if (ma->count >= ma->max) {
-			int err;
-
-			err = tbl_mask_array_realloc(tbl, ma->max +
-						     MASK_ARRAY_SIZE_MIN);
-			if (err) {
-				kfree(mask);
-				return err;
-			}
-
-			ma = ovsl_dereference(tbl->mask_array);
-		}
-
-		for (i = 0; i < ma->max; i++) {
-			const struct sw_flow_mask *t;
-
-			t = ovsl_dereference(ma->masks[i]);
-			if (!t) {
-				rcu_assign_pointer(ma->masks[i], mask);
-				ma->count++;
-				break;
-			}
+		if (tbl_mask_array_add_mask(tbl, mask)) {
+			kfree(mask);
+			return -ENOMEM;
 		}
 	} else {
 		BUG_ON(!mask->ref_count);