Subject: Re: [PATCH/RFC] [v2] TCP: use non-delayed ACK for congestion control RTT

From: Gavin McCullagh <[email-masked]>
Date: Wed, 19 Dec 2007 11:31:25 +0000

Hi,

On Wed, 19 Dec 2007, Ilpo Järvinen wrote:

> Isn't it also much better this way in a case where ACK losses happened,
> taking the longest RTT in that case is clearly questionable as it
> may over-estimate considerably.

Quite so.

> However, another thing to consider is the possibility of this value being 
> used in "timeout-like" fashion in ca modules (I haven't read enough ca 
> modules code to know if any of them does that), on contrary to 
> determinating just rtt or packet's delay in which case this change seems 
> appropriate (most modules do the latter). 

I'm not aware of any, but I haven't read them all either.  I would have
thought tp->srtt was the value to use in this instance, but perhaps the
individual timestamps including delack delay are useful.

> Therefore, if timeout-like module exists one should also add
> TCP_CONG_RTT_STAMP_LONGEST for that particular module and keep using
> seq_rtt for it like previously and use ca_seq_rtt only for others.

Seems reasonable.  I'll add this.

> This part doesn't exists anymore in development tree. Please base this 
> patch (and anything in future) you intend to get included to mainline
> onto net-2.6.25 unless there's a very good reason to not do so or 
> whatever 2.6.xx is the correct net development tree at that time (if
> one exists). Thanks.

Will do.   I gather I should use the latest net- tree in future when
submitting patches.

Thanks for the helpful comments,

Gavin