netdev - Re: [RFC v2] tcp: Export TCP Delayed ACK parameters to user

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Date:	Mon, 31 Oct 2011 22:02:19 +0200
From:	Daniel Baluta <dbaluta@...acom.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, netdev@...r.kernel.org, luto@...capital.net
Subject: Re: [RFC v2] tcp: Export TCP Delayed ACK parameters to user

On Mon, Oct 31, 2011 at 8:10 PM, Rick Jones <rick.jones2@...com> wrote:
> Whether tracked as bytes or segments, my take is that to ask applications to
> have to think about another non-portable socket option is ungood.  I would
> suggest taking the time to work-out the automagic heuristic to drop the
> deferred ACK count on connections where it being large is un-desirable and
> then not need to worry about the limits being global.

Your suggestion deserves further investigation, it looks tricky to
find a good heuristic for increasing/decreasing the ACK deferred count.

>
> Given the stack's existing propensity to try to decide when to increase the
> window I might even go so far as to suggest the sense of the heuristic be
> flipped and it seek to decide when it is ok to increase the number of
> segments/bytes per ACK.  To what extent one needs to go beyond what happens
> already with the stretching of ACKs via GRO/LRO or if that mechanism can
> serve as part of the logic of the heuristic is probably a fertile area for
> discussion.
>
> If I recall correctly, in one of your earlier posts you mentioned something
> about a 20% performance boost.  What were the specific conditions of that
> testing?  Was it over a setup where the receiver already had LRO/GRO or was
> it over a more plain receiver NIC without that functionality?

If I remember correctly on the receiver side there was no LRO/GRO, but we
tweaked some of /proc/sys/net/ipv4 parameters (e.g tcp_rmem).
Also, the traffic was highly unidirectional with many clients feeding multimedia
content to a server.

Anyhow, we used our custom kernel which is an older kernel version.
Are there any recommended benchmarks/tools for testing this kind of parameters?

Daniel.
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