net: sock_rps_record_flow() is for connected sockets
Paolo noticed a cache line miss in UDP recvmsg() to access sk_rxhash, sharing a cache line with sk_drops. sk_drops might be heavily incremented by cpus handling a flood targeting this socket. We might place sk_drops on a separate cache line, but lets try to avoid wasting 64 bytes per socket just for this, since we have other bottlenecks to take care of. sock_rps_record_flow() should only access sk_rxhash for connected flows. Testing sk_state for TCP_ESTABLISHED covers most of the cases for connected sockets, for a zero cost, since system calls using sock_rps_record_flow() also access sk->sk_prot which is on the same cache line. A follow up patch will provide a static_key (Jump Label) since most hosts do not even use RFS. Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Paolo Abeni <pabeni@redhat.com> Acked-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -913,7 +913,17 @@ static inline void sock_rps_record_flow_hash(__u32 hash)
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static inline void sock_rps_record_flow(const struct sock *sk)
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{
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#ifdef CONFIG_RPS
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sock_rps_record_flow_hash(sk->sk_rxhash);
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/* Reading sk->sk_rxhash might incur an expensive cache line miss.
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*
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* TCP_ESTABLISHED does cover almost all states where RFS
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* might be useful, and is cheaper [1] than testing :
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* IPv4: inet_sk(sk)->inet_daddr
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* IPv6: ipv6_addr_any(&sk->sk_v6_daddr)
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* OR an additional socket flag
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* [1] : sk_state and sk_prot are in the same cache line.
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*/
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if (sk->sk_state == TCP_ESTABLISHED)
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sock_rps_record_flow_hash(sk->sk_rxhash);
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#endif
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}
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