[PATCH net-next] tcp: reset timer after any SYNACK retransmit

[PATCH net-next] tcp: reset timer after any SYNACK retransmit

[Yuchung Cheng]

Linux immediately returns SYNACK on (spurious) SYN retransmits, but
keeps the SYNACK timer running independently. Thus the timer may
fire right after the SYNACK retransmit and causes a SYN-SYNACK
cross-fire burst.

Adopt the fast retransmit/recovery idea in established state by
re-arming the SYNACK timer after the fast (SYNACK) retransmit. The
timer may fire late up to 500ms due to the current SYNACK timer wheel,
but it's OK to be conservative when network is congested. Eric's new
listener design should address this issue.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
---
 net/ipv4/tcp_minisocks.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 05eaf89..0f01788 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -551,8 +551,13 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 		 *
 		 * Note that even if there is new data in the SYN packet
 		 * they will be thrown away too.
+		 *
+		 * Reset timer after retransmitting SYNACK, similar to
+		 * the idea of fast retransmit in recovery.
 		 */
-		inet_rtx_syn_ack(sk, req);
+		if (!inet_rtx_syn_ack(sk, req))
+			req->expires = min(TCP_TIMEOUT_INIT << req->num_timeout,
+					   TCP_RTO_MAX) + jiffies;
 		return NULL;
 	}
 
-- 
1.8.2.1

Re: [PATCH net-next] tcp: reset timer after any SYNACK retransmit

[Eric Dumazet]

On Mon, 2013-04-29 at 11:44 -0700, Yuchung Cheng wrote:
> Linux immediately returns SYNACK on (spurious) SYN retransmits, but
> keeps the SYNACK timer running independently. Thus the timer may
> fire right after the SYNACK retransmit and causes a SYN-SYNACK
> cross-fire burst.
> 
> Adopt the fast retransmit/recovery idea in established state by
> re-arming the SYNACK timer after the fast (SYNACK) retransmit. The
> timer may fire late up to 500ms due to the current SYNACK timer wheel,
> but it's OK to be conservative when network is congested. Eric's new
> listener design should address this issue.
> 
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> ---

Acked-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net-next] tcp: reset timer after any SYNACK retransmit

[Neal Cardwell]

On Mon, Apr 29, 2013 at 2:44 PM, Yuchung Cheng <ycheng@google.com> wrote:
> Linux immediately returns SYNACK on (spurious) SYN retransmits, but
> keeps the SYNACK timer running independently. Thus the timer may
> fire right after the SYNACK retransmit and causes a SYN-SYNACK
> cross-fire burst.
>
> Adopt the fast retransmit/recovery idea in established state by
> re-arming the SYNACK timer after the fast (SYNACK) retransmit. The
> timer may fire late up to 500ms due to the current SYNACK timer wheel,
> but it's OK to be conservative when network is congested. Eric's new
> listener design should address this issue.
>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>

Acked-by: Neal Cardwell <ncardwell@google.com>

neal

Re: [PATCH net-next] tcp: reset timer after any SYNACK retransmit

[David Miller]

From: Yuchung Cheng <ycheng@google.com>
Date: Mon, 29 Apr 2013 11:44:51 -0700

> Linux immediately returns SYNACK on (spurious) SYN retransmits, but
> keeps the SYNACK timer running independently. Thus the timer may
> fire right after the SYNACK retransmit and causes a SYN-SYNACK
> cross-fire burst.
> 
> Adopt the fast retransmit/recovery idea in established state by
> re-arming the SYNACK timer after the fast (SYNACK) retransmit. The
> timer may fire late up to 500ms due to the current SYNACK timer wheel,
> but it's OK to be conservative when network is congested. Eric's new
> listener design should address this issue.
> 
> Signed-off-by: Yuchung Cheng <ycheng@google.com>

Applied.

Maybe -stable material?

Re: [PATCH net-next] tcp: reset timer after any SYNACK retransmit

[Yuchung Cheng]

On Mon, Apr 29, 2013 at 12:17 PM, David Miller <davem@davemloft.net> wrote:
> From: Yuchung Cheng <ycheng@google.com>
> Date: Mon, 29 Apr 2013 11:44:51 -0700
>
>> Linux immediately returns SYNACK on (spurious) SYN retransmits, but
>> keeps the SYNACK timer running independently. Thus the timer may
>> fire right after the SYNACK retransmit and causes a SYN-SYNACK
>> cross-fire burst.
>>
>> Adopt the fast retransmit/recovery idea in established state by
>> re-arming the SYNACK timer after the fast (SYNACK) retransmit. The
>> timer may fire late up to 500ms due to the current SYNACK timer wheel,
>> but it's OK to be conservative when network is congested. Eric's new
>> listener design should address this issue.
>>
>> Signed-off-by: Yuchung Cheng <ycheng@google.com>
>
> Applied.
>
> Maybe -stable material?
Should be fine for -stable too. Thanks.