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Date: Sat, 9 Aug 2014 10:15:30 -0700 (PDT) From: Tom Herbert <therbert@...gle.com> To: davem@...emloft.net, netdev@...r.kernel.org cc: eric.dumazet@...il.com Subject: [PATCH v2 net-next] udp: clear rps flow table for packets recv on UDP unconnected sockets This patch addresses a problem posed by Eric Dumazet in RPS/RFS concerning the interaction between connected sockets and traffic on unnconnected sockets. On a server which has both traffic using connected connected sockets and traffic that is going through unconnected UDP sockets, it is very possible that the connected sockets could heavily populate the RPS flow tables. Packets received on unconnected sockets would then be steered based on unrelated entries in the flow tables which leads to suboptimal steering. This happens even if the connections that populate the table are inactive with no traffic, as long as the connected sockets simply remain open unrelated traffic can be steered using that information. This problem would further be exacerbated if the packets on the unconnected UDP sockets are actually part of long lived flows (which apparently would happen with QUIC in their current implementation). This patch clears the RPS flow hash table for packet recieved on unnconnected UDP sockets. The effect is that the "flows" on unconnected socekts will be steered using RPS. We don't do this for unconnected UDP tunnels (encap_rcv) under the assumption that the flow table entries will be adjusted during processing of inner packets. Tested using super_netperf UDP_RR with 200 flows. Did not see any noticeable regression in writing to flow table for every packet. Before fix: 76.99% CPU utilization 112/158/230 90/95/99% latencies 1.62776e+06 tps After fix: 76.03% CPU utilization 115/162/239 90/95/99% latencies 1.62257e+06 tps Signed-off-by: Tom Herbert <therbert@...gle.com> --- net/ipv4/udp.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index f57c0e4..7ba764a 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1444,6 +1444,8 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb) if (inet_sk(sk)->inet_daddr) { sock_rps_save_rxhash(sk, skb); sk_mark_napi_id(sk, skb); + } else { + sock_rps_reset_flow_hash(skb->hash); } rc = sock_queue_rcv_skb(sk, skb); -- 2.0.0.526.g5318336 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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