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authorEric Dumazet <edumazet@google.com>2015-10-02 21:43:35 +0300
committerDavid S. Miller <davem@davemloft.net>2015-10-03 14:32:43 +0300
commitca6fb06518836ef9b65dc0aac02ff97704d52a05 (patch)
tree3fbe433aac9dcf1cae49e6715ced18bd3505d811 /net/ipv4/inet_connection_sock.c
parent1b33bc3e9e903f7293f7dfe80a875b2a5d0305aa (diff)
downloadlinux-ca6fb06518836ef9b65dc0aac02ff97704d52a05.tar.xz
tcp: attach SYNACK messages to request sockets instead of listener
If a listen backlog is very big (to avoid syncookies), then the listener sk->sk_wmem_alloc is the main source of false sharing, as we need to touch it twice per SYNACK re-transmit and TX completion. (One SYN packet takes listener lock once, but up to 6 SYNACK are generated) By attaching the skb to the request socket, we remove this source of contention. Tested: listen(fd, 10485760); // single listener (no SO_REUSEPORT) 16 RX/TX queue NIC Sustain a SYNFLOOD attack of ~320,000 SYN per second, Sending ~1,400,000 SYNACK per second. Perf profiles now show listener spinlock being next bottleneck. 20.29% [kernel] [k] queued_spin_lock_slowpath 10.06% [kernel] [k] __inet_lookup_established 5.12% [kernel] [k] reqsk_timer_handler 3.22% [kernel] [k] get_next_timer_interrupt 3.00% [kernel] [k] tcp_make_synack 2.77% [kernel] [k] ipt_do_table 2.70% [kernel] [k] run_timer_softirq 2.50% [kernel] [k] ip_finish_output 2.04% [kernel] [k] cascade Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/inet_connection_sock.c')
-rw-r--r--net/ipv4/inet_connection_sock.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 80904df02187..099e0ea9242a 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -628,7 +628,7 @@ static void reqsk_queue_hash_req(struct request_sock *req,
* are committed to memory and refcnt initialized.
*/
smp_wmb();
- atomic_set(&req->rsk_refcnt, 2);
+ atomic_set(&req->rsk_refcnt, 2 + 1);
}
void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,