netdev - [PATCH net-next] openvswitch: avoid deferred execution of recirc actions

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Date:   Tue, 13 Sep 2016 10:08:54 -0400
From:   Lance Richardson <lrichard@...hat.com>
To:     netdev@...r.kernel.org, dev@...nvswitch.org
Cc:     pshelar@....org, sramamur@...ux.vnet.ibm.com
Subject: [PATCH net-next] openvswitch: avoid deferred execution of recirc actions

The ovs kernel data path currently defers the execution of all
recirc actions until stack utilization is at a minimum.
This is too limiting for some packet forwarding scenarios due to
the small size of the deferred action FIFO (10 entries). For
example, broadcast traffic sent out more than 10 ports with
recirculation results in packet drops when the deferred action
FIFO becomes full, as reported here:

     http://openvswitch.org/pipermail/dev/2016-March/067672.html

Since the current recursion depth is available (it is already tracked
by the exec_actions_level pcpu variable), we can use it to determine
whether to execute recirculation actions immediately (safe when
recursion depth is low) or defer execution until more stack space is
available.

With this change, the deferred action fifo size becomes a non-issue
for currently failing scenarios because it is no longer used when
there are three or fewer recursions through ovs_execute_actions().

Suggested-by: Pravin Shelar <pshelar@....org>
Signed-off-by: Lance Richardson <lrichard@...hat.com>
---
 net/openvswitch/actions.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 6eb5261..ef7cc6c 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -71,6 +71,8 @@ struct ovs_frag_data {
 static DEFINE_PER_CPU(struct ovs_frag_data, ovs_frag_data_storage);
 
 #define DEFERRED_ACTION_FIFO_SIZE 10
+#define OVS_RECURSION_LIMIT 5
+#define OVS_DEFERRED_ACTION_THRESHOLD (OVS_RECURSION_LIMIT - 2)
 struct action_fifo {
 	int head;
 	int tail;
@@ -78,7 +80,12 @@ struct action_fifo {
 	struct deferred_action fifo[DEFERRED_ACTION_FIFO_SIZE];
 };
 
+struct recirc_keys {
+	struct sw_flow_key key[OVS_DEFERRED_ACTION_THRESHOLD];
+};
+
 static struct action_fifo __percpu *action_fifos;
+static struct recirc_keys __percpu *recirc_keys;
 static DEFINE_PER_CPU(int, exec_actions_level);
 
 static void action_fifo_init(struct action_fifo *fifo)
@@ -1020,6 +1027,7 @@ static int execute_recirc(struct datapath *dp, struct sk_buff *skb,
 			  const struct nlattr *a, int rem)
 {
 	struct deferred_action *da;
+	int level;
 
 	if (!is_flow_key_valid(key)) {
 		int err;
@@ -1043,6 +1051,18 @@ static int execute_recirc(struct datapath *dp, struct sk_buff *skb,
 			return 0;
 	}
 
+	level = this_cpu_read(exec_actions_level);
+	if (level <= OVS_DEFERRED_ACTION_THRESHOLD) {
+		struct recirc_keys *rks = this_cpu_ptr(recirc_keys);
+		struct sw_flow_key *recirc_key = &rks->key[level - 1];
+
+		*recirc_key = *key;
+		recirc_key->recirc_id = nla_get_u32(a);
+		ovs_dp_process_packet(skb, recirc_key);
+
+		return 0;
+	}
+
 	da = add_deferred_actions(skb, key, NULL);
 	if (da) {
 		da->pkt_key.recirc_id = nla_get_u32(a);
@@ -1209,11 +1229,10 @@ int ovs_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			const struct sw_flow_actions *acts,
 			struct sw_flow_key *key)
 {
-	static const int ovs_recursion_limit = 5;
 	int err, level;
 
 	level = __this_cpu_inc_return(exec_actions_level);
-	if (unlikely(level > ovs_recursion_limit)) {
+	if (unlikely(level > OVS_RECURSION_LIMIT)) {
 		net_crit_ratelimited("ovs: recursion limit reached on datapath %s, probable configuration error\n",
 				     ovs_dp_name(dp));
 		kfree_skb(skb);
@@ -1238,10 +1257,17 @@ int action_fifos_init(void)
 	if (!action_fifos)
 		return -ENOMEM;
 
+	recirc_keys = alloc_percpu(struct recirc_keys);
+	if (!recirc_keys) {
+		free_percpu(action_fifos);
+		return -ENOMEM;
+	}
+
 	return 0;
 }
 
 void action_fifos_exit(void)
 {
 	free_percpu(action_fifos);
+	free_percpu(recirc_keys);
 }
-- 
2.5.5