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

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Message-ID: <1319791441.23112.80.camel@edumazet-laptop>
Date:	Fri, 28 Oct 2011 10:44:01 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Baluta <daniel.baluta@...il.com>
Cc:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [RFC] tcp: Export TCP Delayed ACK parameters to user

Le vendredi 28 octobre 2011 à 11:01 +0300, Daniel Baluta a écrit :
> On Fri, Oct 28, 2011 at 3:01 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Le vendredi 28 octobre 2011 à 02:07 +0300, Daniel Baluta a écrit :
> >> RFC2581 ($4.2) specifies when an ACK should be generated as follows:
> >>
> >> " .. an ACK SHOULD be generated for at least every second
> >>   full-sized segment, and MUST be generated within 500 ms
> >>   of the arrival of the first unacknowledged packet.
> >> "
> >>
> >> We export the number of segments and the timeout limits
> >> specified above, so that a user can tune them according
> >> to its needs.
> >>
> >
> > Well, this requires user has a machine exclusive use :)
> 
> So, this means that setting parameters system wide
> isn't an option?
> 

It is a first step, but we can notice a global setting might please one
application but negatively impact other applications.

I guess some users will want a per socket option, but this can come
later. An other idea to save space on socket structures would be to
select two set of values depending on TOS/TCLASS.

I can imagine ssh (lowdelay) and scp (throughput) wanting different
behavior here.

> On Windows there is a global setting TcpAckFrequency [1],
> which is similar with our tcp_delack_{min,max}.
> 
> On Solaris there is a global option tcp_deferred_acks_max [2],
> which is similar with our tcp_delack_segs.
> 

and also has tcp_deferred_ack_interval

> Thanks for your comments, I will post an updated patch asap.
> 
> Daniel.
> 
> [1] http://support.microsoft.com/kb/328890
> [2] http://www.sean.de/Solaris/soltune.html

Dont forget to CC Andy Lutomirski <luto@...capital.net>, he might be
interested being part of the process.

Thanks


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