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ipv4: tcp: set SOCK_USE_WRITE_QUEUE for ip_send_unicast_reply()
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TCP uses per cpu 'sockets' to send some packets :
- RST packets ( tcp_v4_send_reset()) )
- ACK packets for SYN_RECV and TIMEWAIT sockets

By setting SOCK_USE_WRITE_QUEUE flag, we tell sock_wfree()
to not call sk_write_space() since these internal sockets
do not care.

This gives a small performance improvement, merely by allowing
cpu to properly predict the sock_wfree() conditional branch,
and avoiding one atomic operation.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Apr 5, 2016
1 parent 9caad86 commit a9d6532
Showing 1 changed file with 1 addition and 0 deletions.
1 change: 1 addition & 0 deletions net/ipv4/tcp_ipv4.c
Original file line number Diff line number Diff line change
Expand Up @@ -2384,6 +2384,7 @@ static int __net_init tcp_sk_init(struct net *net)
IPPROTO_TCP, net);
if (res)
goto fail;
sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);
*per_cpu_ptr(net->ipv4.tcp_sk, cpu) = sk;
}

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