path: root/net/ipv4/tcp_fastopen.c
diff options
authorEric Dumazet <edumazet@google.com>2015-10-02 11:43:35 -0700
committerDavid S. Miller <davem@davemloft.net>2015-10-03 04:32:43 -0700
commitca6fb06518836ef9b65dc0aac02ff97704d52a05 (patch)
tree3fbe433aac9dcf1cae49e6715ced18bd3505d811 /net/ipv4/tcp_fastopen.c
parentipv6: remove obsolete inet6 functions (diff)
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/tcp_fastopen.c')
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index f69f436fcbcc..410ac481fda0 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -161,13 +161,13 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
/* Activate the retrans timer so that SYNACK can be retransmitted.
- * The request socket is not added to the SYN table of the parent
+ * The request socket is not added to the ehash
* because it's been added to the accept queue directly.
inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
- atomic_set(&req->rsk_refcnt, 1);
+ atomic_set(&req->rsk_refcnt, 2);
/* Add the child socket directly into the accept queue */
inet_csk_reqsk_queue_add(sk, req, child);