* [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path
@ 2013-03-04 16:23 Neal Cardwell
2013-03-04 16:55 ` Eric Dumazet
0 siblings, 1 reply; 3+ messages in thread
From: Neal Cardwell @ 2013-03-04 16:23 UTC (permalink / raw)
To: David Miller; +Cc: edumazet, ycheng, nanditad, netdev, Neal Cardwell
We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
before and after going to step5. That wastes CPU and double-counts the
receiver-side RTT sample.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
---
net/ipv4/tcp_input.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a759e19..0d9bdac 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5485,6 +5485,9 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
if (tcp_checksum_complete_user(sk, skb))
goto csum_error;
+ if ((int)skb->truesize > sk->sk_forward_alloc)
+ goto step5;
+
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
@@ -5496,9 +5499,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
tcp_rcv_rtt_measure_ts(sk, skb);
- if ((int)skb->truesize > sk->sk_forward_alloc)
- goto step5;
-
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
/* Bulk data transfer: receiver */
--
1.8.1.3
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path
2013-03-04 16:23 [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path Neal Cardwell
@ 2013-03-04 16:55 ` Eric Dumazet
2013-03-04 19:16 ` David Miller
0 siblings, 1 reply; 3+ messages in thread
From: Eric Dumazet @ 2013-03-04 16:55 UTC (permalink / raw)
To: Neal Cardwell; +Cc: David Miller, edumazet, ycheng, nanditad, netdev
On Mon, 2013-03-04 at 11:23 -0500, Neal Cardwell wrote:
> We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
> before and after going to step5. That wastes CPU and double-counts the
> receiver-side RTT sample.
>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> ---
> net/ipv4/tcp_input.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index a759e19..0d9bdac 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5485,6 +5485,9 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
> if (tcp_checksum_complete_user(sk, skb))
> goto csum_error;
>
> + if ((int)skb->truesize > sk->sk_forward_alloc)
> + goto step5;
> +
> /* Predicted packet is in window by definition.
> * seq == rcv_nxt and rcv_wup <= rcv_nxt.
> * Hence, check seq<=rcv_wup reduces to:
> @@ -5496,9 +5499,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
>
> tcp_rcv_rtt_measure_ts(sk, skb);
>
> - if ((int)skb->truesize > sk->sk_forward_alloc)
> - goto step5;
> -
> NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
>
> /* Bulk data transfer: receiver */
Acked-by: Eric Dumazet <edumazet@google.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path
2013-03-04 16:55 ` Eric Dumazet
@ 2013-03-04 19:16 ` David Miller
0 siblings, 0 replies; 3+ messages in thread
From: David Miller @ 2013-03-04 19:16 UTC (permalink / raw)
To: eric.dumazet; +Cc: ncardwell, edumazet, ycheng, nanditad, netdev
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 04 Mar 2013 08:55:33 -0800
> On Mon, 2013-03-04 at 11:23 -0500, Neal Cardwell wrote:
>> We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
>> before and after going to step5. That wastes CPU and double-counts the
>> receiver-side RTT sample.
>>
>> Signed-off-by: Neal Cardwell <ncardwell@google.com>
...
> Acked-by: Eric Dumazet <edumazet@google.com>
Applied and queued up for -stable.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-03-04 16:23 [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path Neal Cardwell
2013-03-04 16:55 ` Eric Dumazet
2013-03-04 19:16 ` David Miller
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