Tweaks for high-bandwidth tinc

[Brandon Black]

On Fri, Nov 12, 2010 at 5:18 PM, Guus Sliepen <guus at tinc-vpn.org> wrote:
> On Fri, Nov 12, 2010 at 12:43:41PM -0600, Brandon Black wrote:
>> Another thing we get hit with (thanks to the underlying network at
>> Amazon under brutal conditions, I think) is isolated packets jumping
>> the queue by a lot.  E.g. in a given tunnel's sequence, we might see
>> 1-2 packets suddenly arrive hundreds of seqnos ahead of the most
>> recent seqno, but then they're immediately followed by all of the
>> "missing" packets (many of which would then be dropped by tinc by
>> default).
>
> Aha. How often does that happen?

Not very often in terms of packet percentage I guess, but pretty
frequently in the absolute sense.  I've attached a syslog snippet from
when I was running with a 512-packet late/replay window + the
queue-jumper fix discussed, and had the warning messages split out and
reworded to help me understand what was going on.  You can see in the
snippet several examples of single future packets that were dropped,
as well as one instance where it was true loss (it dropped 16 packets
(1/32 of my 512 window) and then gave up and did the fast-forward).
I've made this stuff the last patch in the series, since it's the most
questionable one.

> I think all of this can be merged. Each feature in its own patch would be very
> nice, the order is less important.

Patches inbound to the list now.  This is my first time trying out git
format-patches + send-email (and via gmail), hopefully it comes out ok
:)

Note that while the patches were created against the latest repository
source, they were only tested by me in production by applying them
(with some patch fuzz-factor involved) to the Ubuntu Maverick 1.0.13-1
package source and making a custom package of that for my own use.
It's possible some of the intervening repo changes could interfere
with the patches in some way.

-- Brandon
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