Re: [PATCH] tcp: ack when we get an OOO/lost packet

[Andrei Borzenkov]

12.08.2015 18:16, Josef Bacik пишет:
> While adding tcp window scaling support I was finding that I'd get some packet
> loss or reordering when transferring from large distances and grub would just
> timeout.  This is because we weren't ack'ing when we got our OOO packet, so 
> the
> sender didn't know it needed to retransmit anything, so eventually it would 
> fill
> the window and stop transmitting, and we'd time out.  Fix this by ACK'ing when
> we don't find our next sequence numbered packet.  With this fix I no longer 
> time
> out.  Thanks,
> 

Applied. Sorry, it somehow slipped through.

More ideas in the same direction.

1. GRUB timeout for receiving currently is ~33 seconds. It is too small
comparing with anything else. I am pretty sure in situation from tcpdump
you sent me we could recover if timeout was in order of several minutes :)

2. We may consider sending ACK in grub_net_tcp_retransmit()
additionally, although it probably needs proper rate-limiting based on RTT.

3. Using timestamp option may improve RTT detection for partner and is
pretty cheap to implement.

> Signed-off-by: Josef Bacik <address@hidden>
> ---
>  grub-core/net/tcp.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/grub-core/net/tcp.c b/grub-core/net/tcp.c
> index 25720b1..6b411dd 100644
> --- a/grub-core/net/tcp.c
> +++ b/grub-core/net/tcp.c
> @@ -902,7 +902,10 @@ grub_net_recv_tcp_packet (struct grub_net_buff *nb,
>         grub_priority_queue_pop (sock->pq);
>       }
>        if (grub_be_to_cpu32 (tcph->seqnr) != sock->their_cur_seq)
> -     return GRUB_ERR_NONE;
> +     {
> +       ack (sock);
> +       return GRUB_ERR_NONE;
> +     }
>        while (1)
>       {
>         nb_top_p = grub_priority_queue_top (sock->pq);
>