diff options
| author | Eric Dumazet <edumazet@google.com> | 2016-12-07 04:32:50 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-12-07 16:47:35 +0100 |
| commit | 5b8e2f61b9df529ca4af057daf7bfb1de348bdf1 (patch) | |
| tree | ccd2569b8eb1ab8267667f690370ee79ccf5916f /include/net | |
| parent | tun: Use netif_receive_skb instead of netif_rx (diff) | |
| download | linux-5b8e2f61b9df529ca4af057daf7bfb1de348bdf1.tar.xz linux-5b8e2f61b9df529ca4af057daf7bfb1de348bdf1.zip | |
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>
Diffstat (limited to 'include/net')
| -rw-r--r-- | include/net/sock.h | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/include/net/sock.h b/include/net/sock.h index 6dfe3aa22b97..1749e38d0301 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -913,7 +913,17 @@ static inline void sock_rps_record_flow_hash(__u32 hash) static inline void sock_rps_record_flow(const struct sock *sk) { #ifdef CONFIG_RPS - sock_rps_record_flow_hash(sk->sk_rxhash); + /* Reading sk->sk_rxhash might incur an expensive cache line miss. + * + * TCP_ESTABLISHED does cover almost all states where RFS + * might be useful, and is cheaper [1] than testing : + * IPv4: inet_sk(sk)->inet_daddr + * IPv6: ipv6_addr_any(&sk->sk_v6_daddr) + * OR an additional socket flag + * [1] : sk_state and sk_prot are in the same cache line. + */ + if (sk->sk_state == TCP_ESTABLISHED) + sock_rps_record_flow_hash(sk->sk_rxhash); #endif } |