[ovs-discuss] [PATCH-RFC 2/2] Improve ARP latency

[dwilder at us.ibm.com]

skb_get_hash() returns a 0 (invalid hash) for arp packets resulting in same
ids_index for every arp packet. This results in a single ovs-vswitchd handler
thread processing every arp packet severely impacting the average latency of
arps. This change spreads the work evenly between all the handler threads.


  datapath/vport.c | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/datapath/vport.c b/datapath/vport.c
index 024491f..20d20fa 100644
--- a/datapath/vport.c
+++ b/datapath/vport.c
@@ -465,6 +465,12 @@ u32 ovs_vport_find_upcall_portid(const struct  
vport *vport, struct sk_buff *skb)
  	if (ids->n_ids == 1 && ids->ids[0] == 0)
  		return 0;

+	/* skb_get_hash() is not supporting ETH_P_ARP packets returning a 0
+	 * (invalid hash) for every ARP.
+	 */
+	if (skb->protocol == ntohs(ETH_P_ARP))
+		return ids->ids[vport->port_no%ids->n_ids];
+
  	hash = skb_get_hash(skb);
  	return ids->ids[hash - ids->n_ids * reciprocal_divide(hash, ids->rn_ids)];
  }
--