[PATCH] Add a new TCP_IGNOREIDLE socket option

[Andre Oppermann]

On 12.02.2013 11:55, Andrey Zonov wrote:
> On 2/11/13 3:18 PM, Andre Oppermann wrote:
>>
>> Smaller RTO (1s) has become a RFC so there was very broad consensus in
>> TCPM that is a good thing.  We don't have it yet because we were not fully
>> compliant in one case (loss of first segment).  I've fixed that a while
>> back and will bring 1s RTO soon to HEAD.
>>
>
> They use 300ms at least for me/my link/ISP/etc.

Let me be more precise: An initial RTO of 1s was published as RFC.  This
is what I'm referring to.  It affects the setup phase of a connection.

A separate issue is the minimum RTO during a connection.  According to
the RFC the RTO during the lifetime of the connection should also not be
less than 1s.  The RTO being determined based on the RTT measurement done
using timestamps or Karn's algorithm.  However on fast links this has been
shown to be too long to wait for.  So FreeBSD decreased the allowed lower
bound to hz/33.  This is only effective if your RTO was actually calculated
to be equal or lower than that.  The result is a quicker re-probing and
discovery of the current line conditions.  Since the RTO was measured to be
less-equal than hz/33, the possible negative downside is very limited.

-- 
Andre