[PATCH net-next v2 1/1] net: openvswitch: Use on stack sw_flow_key in ovs_packet_cmd_execute

[Eddy Tao]

Use on stack sw_flow_key in ovs_packet_cmd_execute

Reason: As key function in slow-path, ovs_packet_cmd_execute and
        ovs_flow_cmd_new allocate transient memory for sw_flow
        and frees it at the end of function.
        The procedure is not efficient in 2 aspects
        1. actuall sw_flow_key is what the function need
        2. free/alloc involves kmem_cache operations
        when system under frequent slow path operation

        Existing code in ovs_flow_cmd_new/set/get use stack
        to store sw_flow_mask and sw_flow_key deliberately

Performance benefit:
        ovs_packet_cmd_execute efficiency improved
        Avoid 2 calls to kmem_cache alloc
        Avoid memzero of 200 bytes
        6% less instructions

Testing topology
            +-----+
      nic1--|     |--nic1
      nic2--|     |--nic2
VM1(16cpus) | ovs |   VM2(16 cpus)
      nic3--|4cpus|--nic3
      nic4--|     |--nic4
            +-----+
   2 threads on each vnic with affinity set on client side

netperf -H $peer -p $((port+$i)) -t UDP_RR  -l 60 -- -R 1 -r 8K,8K
netperf -H $peer -p $((port+$i)) -t TCP_RR  -l 60 -- -R 1 -r 120,240
netperf -H $peer -p $((port+$i)) -t TCP_CRR -l 60 -- -R 1 -r 120,240

Before the fix
      Mode Iterations   Variance    Average
    UDP_RR         10      %1.31      46724
    TCP_RR         10      %6.26      77188
   TCP_CRR         10      %0.10      20505
UDP_STREAM         10      %4.55      19907
TCP_STREAM         10      %9.93      28942

After the fix
      Mode Iterations   Variance    Average
    UDP_RR         10      %1.51      49097
    TCP_RR         10      %5.58      78540
   TCP_CRR         10      %0.14      20542
UDP_STREAM         10     %11.17      22532
TCP_STREAM         10     %11.14      28579

Signed-off-by: Eddy Tao <taoyuan_eddy@xxxxxxxxxxx>
---
 V1 -> V2: Further reduce memory usage by using sw_flow_key instead
           of sw_flow, revise description of change and provide data

 net/openvswitch/datapath.c | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index fcee6012293b..ae3146d51079 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -596,8 +596,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 	struct nlattr **a = info->attrs;
 	struct sw_flow_actions *acts;
 	struct sk_buff *packet;
-	struct sw_flow *flow;
-	struct sw_flow_actions *sf_acts;
+	struct sw_flow_key key;
 	struct datapath *dp;
 	struct vport *input_vport;
 	u16 mru = 0;
@@ -636,24 +635,20 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	/* Build an sw_flow for sending this packet. */
-	flow = ovs_flow_alloc();
-	err = PTR_ERR(flow);
-	if (IS_ERR(flow))
-		goto err_kfree_skb;
+	memset(&key, 0, sizeof(key));
 
 	err = ovs_flow_key_extract_userspace(net, a[OVS_PACKET_ATTR_KEY],
-					     packet, &flow->key, log);
+					     packet, &key, log);
 	if (err)
-		goto err_flow_free;
+		goto err_kfree_skb;
 
 	err = ovs_nla_copy_actions(net, a[OVS_PACKET_ATTR_ACTIONS],
-				   &flow->key, &acts, log);
+				   &key, &acts, log);
 	if (err)
-		goto err_flow_free;
+		goto err_kfree_skb;
 
-	rcu_assign_pointer(flow->sf_acts, acts);
-	packet->priority = flow->key.phy.priority;
-	packet->mark = flow->key.phy.skb_mark;
+	packet->priority = key.phy.priority;
+	packet->mark = key.phy.skb_mark;
 
 	rcu_read_lock();
 	dp = get_dp_rcu(net, ovs_header->dp_ifindex);
@@ -661,7 +656,7 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 	if (!dp)
 		goto err_unlock;
 
-	input_vport = ovs_vport_rcu(dp, flow->key.phy.in_port);
+	input_vport = ovs_vport_rcu(dp, key.phy.in_port);
 	if (!input_vport)
 		input_vport = ovs_vport_rcu(dp, OVSP_LOCAL);
 
@@ -670,20 +665,17 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb, struct genl_info *info)
 
 	packet->dev = input_vport->dev;
 	OVS_CB(packet)->input_vport = input_vport;
-	sf_acts = rcu_dereference(flow->sf_acts);
 
 	local_bh_disable();
-	err = ovs_execute_actions(dp, packet, sf_acts, &flow->key);
+	err = ovs_execute_actions(dp, packet, acts, &key);
 	local_bh_enable();
 	rcu_read_unlock();
 
-	ovs_flow_free(flow, false);
+	ovs_nla_free_flow_actions(acts);
 	return err;
 
 err_unlock:
 	rcu_read_unlock();
-err_flow_free:
-	ovs_flow_free(flow, false);
 err_kfree_skb:
 	kfree_skb(packet);
 err:
-- 
2.27.0