Re: [PATCH] tcp: avoid cwnd moderation in undo

On Mon, Mar 14, 2011 at 3:10 PM, Yuchung Cheng [off-list ref] wrote:

On Mon, Mar 14, 2011 at 3:06 AM, Carsten Wolff [off-list ref] wrote:

quoted

The moderation is in place to avoid gigantic segment bursts, which could cause
unnecessary pressure on buffers. In my eyes it's already suboptimal that the
moderation is weakened in the presence of (detected) reordering, let alone
removing it completely.

In the presence of reordering, cwnd is already moderated in Disorder
state before
 entering the (false) recovery.

I've always been somewhat skeptical of the usefulness of cwnd
moderation.  First, I don't know that its behavior is well defined.
When *should* tcp_moderate_cwnd() actually be called, and why?

Second, I've never liked the idea in general.  Reducing cwnd has an
effect lasting many RTTs, so reducing it in response to a transient
event like reordering seems dubious.  And it does not address many
causes of bursts, such as ack compression or stretch acks.

  -John