[PATCH net-next] tcp: fix no cwnd growth after timeout

[PATCH net-next] tcp: fix no cwnd growth after timeout

[Yuchung Cheng]

In commit 0f7cc9a3 "tcp: increase throughput when reordering is high",
it only allows cwnd to increase in Open state. This mistakenly disables
slow start after timeout (CA_Loss). Moreover cwnd won't grow if the
state moves from Disorder to Open later in tcp_fastretrans_alert().

Therefore the correct logic should be to allow cwnd to grow as long
as the data is received in order in Open, Loss, or even Disorder state.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
---
 net/ipv4/tcp_input.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1969e16..894bc17 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3162,16 +3162,14 @@ static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 
 	/* If reordering is high then always grow cwnd whenever data is
 	 * delivered regardless of its ordering. Otherwise stay conservative
-	 * and only grow cwnd on in-order delivery in Open state, and retain
-	 * cwnd in Disordered state (RFC5681). A stretched ACK with
+	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
 	 * new SACK or ECE mark may first advance cwnd here and later reduce
 	 * cwnd in tcp_fastretrans_alert() based on more states.
 	 */
 	if (tcp_sk(sk)->reordering > sysctl_tcp_reordering)
 		return flag & FLAG_FORWARD_PROGRESS;
 
-	return inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
-	       flag & FLAG_DATA_ACKED;
+	return flag & FLAG_DATA_ACKED;
 }
 
 /* Check that window update is acceptable.
-- 
1.8.4

Re: [PATCH net-next] tcp: fix no cwnd growth after timeout

[Neal Cardwell]

On Thu, Sep 5, 2013 at 6:36 PM, Yuchung Cheng <ycheng@google.com> wrote:
> In commit 0f7cc9a3 "tcp: increase throughput when reordering is high",
> it only allows cwnd to increase in Open state. This mistakenly disables
> slow start after timeout (CA_Loss). Moreover cwnd won't grow if the
> state moves from Disorder to Open later in tcp_fastretrans_alert().
>
> Therefore the correct logic should be to allow cwnd to grow as long
> as the data is received in order in Open, Loss, or even Disorder state.
>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>

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

neal

Re: [PATCH net-next] tcp: fix no cwnd growth after timeout

[David Miller]

From: Neal Cardwell <ncardwell@google.com>
Date: Thu, 5 Sep 2013 19:56:59 -0400

> On Thu, Sep 5, 2013 at 6:36 PM, Yuchung Cheng <ycheng@google.com> wrote:
>> In commit 0f7cc9a3 "tcp: increase throughput when reordering is high",
>> it only allows cwnd to increase in Open state. This mistakenly disables
>> slow start after timeout (CA_Loss). Moreover cwnd won't grow if the
>> state moves from Disorder to Open later in tcp_fastretrans_alert().
>>
>> Therefore the correct logic should be to allow cwnd to grow as long
>> as the data is received in order in Open, Loss, or even Disorder state.
>>
>> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> 
> Acked-by: Neal Cardwell <ncardwell@google.com>

Applied, thank you.