netdev - Re: Can I limit the number of active tx per TCP socket?

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Date:	Thu, 06 Mar 2014 11:27:06 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	David Laight <David.Laight@...lab.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Can I limit the number of active tx per TCP socket?

On Thu, 2014-03-06 at 11:06 -0800, Rick Jones wrote:
> On 03/06/2014 10:09 AM, Neal Cardwell wrote:
> > Eric's recent "auto corking" feature may be helpful in this context:
> >
> >    http://lwn.net/Articles/576263/
> 
> Doesn't that depend on the bottleneck being local to the sending side? 
> Perhaps I've mis-understood David's setup, but I get the impression the 
> bottleneck is not at the sending side but either in the middle or at the 
> end, so tx completions will still be happening quickly.

There were multiple aspects.

One skb per flow in qdisc/TX ring : TCP Small Queue spirit (recently
kind of broken by commit 98e09386c0ef4dfd ("tcp: tsq: restore minimal
amount of queueing ")

FQ adds the Fairness part (bulk flows wont slow down interactive flows)

Then if the problem is having a high speed interface on the sender,
and a low speed receiver (or bottleneck), then SO_MAX_PACING_RATE is an
easy way to solve the problem. Only flows setting this option will be
paced, while others can use all the bandwidth they need.




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