net/mlx5: DR, For short chains of STEs, avoid allocating ste_arr dynamically

While creating rule, ste_arr is an array that is allocated at the start
of the function and freed at the end.
This memory allocation can sometimes lead to "hiccups" of up to 10ms.
However, the common use case is short chains of STEs. For such cases,
we can use a local buffer on stack instead.

Changes in v2:
  Use small local array for short rules, allocate dynamically for long rules
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c

@@ -3,7 +3,8 @@
 
 #include "dr_types.h"
 
-#define DR_RULE_MAX_STE_CHAIN (DR_RULE_MAX_STES + DR_ACTION_MAX_STES)
+#define DR_RULE_MAX_STES_OPTIMIZED 5
+#define DR_RULE_MAX_STE_CHAIN_OPTIMIZED (DR_RULE_MAX_STES_OPTIMIZED + DR_ACTION_MAX_STES)
 
 static int dr_rule_append_to_miss_list(struct mlx5dr_ste_ctx *ste_ctx,
 				       struct mlx5dr_ste *new_last_ste,
@@ -1089,6 +1090,7 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 			size_t num_actions,
 			struct mlx5dr_action *actions[])
 {
+	u8 hw_ste_arr_optimized[DR_RULE_MAX_STE_CHAIN_OPTIMIZED * DR_STE_SIZE] = {};
 	struct mlx5dr_ste_send_info *ste_info, *tmp_ste_info;
 	struct mlx5dr_matcher *matcher = rule->matcher;
 	struct mlx5dr_domain *dmn = matcher->tbl->dmn;
@@ -1098,6 +1100,7 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 	struct mlx5dr_ste_htbl *cur_htbl;
 	struct mlx5dr_ste *ste = NULL;
 	LIST_HEAD(send_ste_list);
+	bool hw_ste_arr_is_opt;
 	u8 *hw_ste_arr = NULL;
 	u32 new_hw_ste_arr_sz;
 	int ret, i;
@@ -1109,9 +1112,23 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 			 rule->flow_source))
 		return 0;
 
-	hw_ste_arr = kzalloc(DR_RULE_MAX_STE_CHAIN * DR_STE_SIZE, GFP_KERNEL);
+	ret = mlx5dr_matcher_select_builders(matcher,
+					     nic_matcher,
+					     dr_rule_get_ipv(&param->outer),
+					     dr_rule_get_ipv(&param->inner));
+	if (ret)
+		return ret;
+
+	hw_ste_arr_is_opt = nic_matcher->num_of_builders <= DR_RULE_MAX_STES_OPTIMIZED;
+	if (likely(hw_ste_arr_is_opt)) {
+		hw_ste_arr = hw_ste_arr_optimized;
+	} else {
+		hw_ste_arr = kzalloc((nic_matcher->num_of_builders + DR_ACTION_MAX_STES) *
+				     DR_STE_SIZE, GFP_KERNEL);
+
 		if (!hw_ste_arr)
 			return -ENOMEM;
+	}
 
 	mlx5dr_domain_nic_lock(nic_dmn);
 
@@ -1119,13 +1136,6 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 	if (ret)
 		goto free_hw_ste;
 
-	ret = mlx5dr_matcher_select_builders(matcher,
-					     nic_matcher,
-					     dr_rule_get_ipv(&param->outer),
-					     dr_rule_get_ipv(&param->inner));
-	if (ret)
-		goto remove_from_nic_tbl;
-
 	/* Set the tag values inside the ste array */
 	ret = mlx5dr_ste_build_ste_arr(matcher, nic_matcher, param, hw_ste_arr);
 	if (ret)
@@ -1187,6 +1197,7 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 
 	mlx5dr_domain_nic_unlock(nic_dmn);
 
+	if (unlikely(!hw_ste_arr_is_opt))
 		kfree(hw_ste_arr);
 
 	return 0;
@@ -1204,7 +1215,10 @@ dr_rule_create_rule_nic(struct mlx5dr_rule *rule,
 
 free_hw_ste:
 	mlx5dr_domain_nic_unlock(nic_dmn);
+
+	if (unlikely(!hw_ste_arr_is_opt))
 		kfree(hw_ste_arr);
+
 	return ret;
 }