Re: [PATCH] tcp: Implement a two-level initial RTO as per draft RFC 2988bis-02.

From: tsuna <redacted>
Date: Wed, 18 May 2011 20:56:33 -0700

On Wed, May 18, 2011 at 7:36 PM, David Miller [off-list ref] wrote:

quoted

From: Benoit Sigoure <redacted>
Date: Wed, 18 May 2011 19:22:24 -0700

quoted

Prior to this patch, Linux would always use 3 seconds (compile-time
constant) as the initial RTO.  Draft RFC 2988bis-02 proposes to tune
this down to 1 second and, in case of a timeout during the TCP 3WHS,
revert the RTO back up to 3 seconds when data transmission begins.

We just had a discussion where it was determined that changes to
these settings are "network specific" and therefore that if it
is appropriate at all (I'm still not convinced) it is only suitable
as a routing metric.

Fair enough.  I'll take another stab at it and see if I can change
this to be on a per network basis.  Do I need any patch that's not yet
in Linus' tree?  I'm referring to this:

Keep in mind another thing I do not like about this knob.

The IETF draft has a requirement that we fallback to 3 seconds if the
initial RTO is 1 second.

Nothing in your facilities ensure this, or provide a way for the
kernel to make sure this is the case.

And for other values of initial RTO, what fallback is appropriate?

As a result of all of this, I do not really think this is something
the user should control at all.

I really would rather see the initial RTO be static and be set to 1
with fallback RTO of 3.