Re: [PATCH net-next 1/2] tcp: Carry txstamp_ack in tcp_fragment_tstamp

[Soheil Hassas Yeganeh <soheil@google.com>]

On Wed, Apr 20, 2016 at 1:50 AM, Martin KaFai Lau <kafai@fb.com> wrote:
> When a tcp skb is sliced into two smaller skbs (e.g. in
> tcp_fragment() and tso_fragment()),  it does not carry
> the txstamp_ack bit to the newly created skb if it is needed.
> The end result is a timestamping event (SCM_TSTAMP_ACK) will
> be missing from the sk->sk_error_queue.
>
> This patch carries this bit to the new skb2
> in tcp_fragment_tstamp().
>
> BPF Output Before:
> ~~~~~~
> <No output due to missing SCM_TSTAMP_ACK timestamp>
>
> BPF Output After:
> ~~~~~~
> <...>-2050  [000] d.s.   100.928763: : ee_data:14599
>
> Packetdrill Script:
> ~~~~~~
> +0 `sysctl -q -w net.ipv4.tcp_min_tso_segs=10`
> +0 `sysctl -q -w net.ipv4.tcp_no_metrics_save=1`
> +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> +0 bind(3, ..., ...) = 0
> +0 listen(3, 1) = 0
>
> 0.100 < S 0:0(0) win 32792 <mss 1460,sackOK,nop,nop,nop,wscale 7>
> 0.100 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 7>
> 0.200 < . 1:1(0) ack 1 win 257
> 0.200 accept(3, ..., ...) = 4
> +0 setsockopt(4, SOL_TCP, TCP_NODELAY, [1], 4) = 0
>
> +0 setsockopt(4, SOL_SOCKET, 37, [2688], 4) = 0
> 0.200 write(4, ..., 14600) = 14600
> +0 setsockopt(4, SOL_SOCKET, 37, [2176], 4) = 0
>
> 0.200 > . 1:7301(7300) ack 1
> 0.200 > P. 7301:14601(7300) ack 1
>
> 0.300 < . 1:1(0) ack 14601 win 257
>
> 0.300 close(4) = 0
> 0.300 > F. 14601:14601(0) ack 1
> 0.400 < F. 1:1(0) ack 16062 win 257
> 0.400 > . 14602:14602(0) ack 2
>
> Signed-off-by: Martin KaFai Lau <kafai@fb.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Neal Cardwell <ncardwell@google.com>
> Cc: Soheil Hassas Yeganeh <soheil@google.com>
> Cc: Willem de Bruijn <willemb@google.com>
> Cc: Yuchung Cheng <ycheng@google.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Tested-by: Soheil Hassas Yeganeh <soheil@google.com>
> ---
>  net/ipv4/tcp_output.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 96182a2..f7c3bc0 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1123,6 +1123,8 @@ static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
>                 shinfo->tx_flags &= ~tsflags;
>                 shinfo2->tx_flags |= tsflags;
>                 swap(shinfo->tskey, shinfo2->tskey);
> +               TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
> +               TCP_SKB_CB(skb)->txstamp_ack = 0;
>         }
>  }
>
> --
> 2.5.1
>