netdev - Re: TCP: Support configurable delayed-ack parameters

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Message-ID: <1393602573.26794.65.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 28 Feb 2014 07:49:33 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Harout Hedeshian <harouth@...eaurora.org>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: TCP: Support configurable delayed-ack parameters

On Fri, 2014-02-28 at 08:14 -0700, Harout Hedeshian wrote:
> Hello David,
> 
> I found a thread from June 2012 (subject matches this email) discussing the
> addition of parameters to manually tune the delayed TCP ACK parameters, and
> add new TCP socket options for application specific tuning. The patch in
> question would multiply the receive mss by some constant exposed in /proc.
> We have experimented with a similar approach and found significant
> improvements in performance when asymmetric links are utilized; specifically
> where the hardware is limited in egress packets/sec (but not raw bandwidth).
> As an example, in one test we saw a 100% improvement when doing rcv_mss*4.

Note that we have some bugs in TCP stack, that might explain the
behavior. Please post pcap so that we can really understand your point,
and eventually pinpoint bugs.

For example TSO should_defer() is known to be problematic, and we have a
patch fixing the issue. I'll post it today.

Other bugs included a problem in TCP Small Queue, that was recently
fixed.



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