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

[Josef Bacik]

On 12/07/2015 12:59 PM, Andrei Borzenkov wrote:
> 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 :)

Yeah I jacked up the receive timeout in one of my iterations and that 
helped as well.  Could probably make it configurable.

> 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.

I'm trying to get some standard testing set up internally so I can test 
all of our hardware types whenever I make changes.  Once I get that 
stuff set up I'll look at adding this and some other features.  Thanks,

Josef