Re: [PATCH v2 net-next] tcp: enhance tcp collapsing

[Neal Cardwell <ncardwell@google.com>]

On Tue, Nov 1, 2016 at 1:53 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> As Ilya Lesokhin suggested, we can collapse two skbs at retransmit
> time even if the skb at the right has fragments.
>
> We simply have to use more generic skb_copy_bits() instead of
> skb_copy_from_linear_data() in tcp_collapse_retrans()
>
> Also need to guard this skb_copy_bits() in case there is nothing to
> copy, otherwise skb_put() could panic if left skb has frags.
>
> Tested:
>
> Used following packetdrill test
>
> // Establish a connection.
> 0.000 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 < S 0:0(0) win 32792 <mss 1460,sackOK,nop,nop,nop,wscale 8>
>    +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
> +.100 < . 1:1(0) ack 1 win 257
>    +0 accept(3, ..., ...) = 4
>
>    +0 setsockopt(4, SOL_TCP, TCP_NODELAY, [1], 4) = 0
>    +0 write(4, ..., 200) = 200
>    +0 > P. 1:201(200) ack 1
> +.001 write(4, ..., 200) = 200
>    +0 > P. 201:401(200) ack 1
> +.001 write(4, ..., 200) = 200
>    +0 > P. 401:601(200) ack 1
> +.001 write(4, ..., 200) = 200
>    +0 > P. 601:801(200) ack 1
> +.001 write(4, ..., 200) = 200
>    +0 > P. 801:1001(200) ack 1
> +.001 write(4, ..., 100) = 100
>    +0 > P. 1001:1101(100) ack 1
> +.001 write(4, ..., 100) = 100
>    +0 > P. 1101:1201(100) ack 1
> +.001 write(4, ..., 100) = 100
>    +0 > P. 1201:1301(100) ack 1
> +.001 write(4, ..., 100) = 100
>    +0 > P. 1301:1401(100) ack 1
>
> +.100 < . 1:1(0) ack 1 win 257 <nop,nop,sack 1001:1401>
> // Check that TCP collapse works :
>    +0 > P. 1:1001(1000) ack 1
>
>
> Reported-by: Ilya Lesokhin <ilyal@mellanox.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Neal Cardwell <ncardwell@google.com>
> Cc: Yuchung Cheng <ycheng@google.com>
> Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
> ---

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

Thanks, Eric. :-)

neal