netdev - Re: [PATCH net-2.6 1/2] [TCP]: Fix ratehalving with bidirectional flows

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Message-ID: <Pine.LNX.4.64.0707310751260.15079@kivilampi-30.cs.helsinki.fi>
Date:	Tue, 31 Jul 2007 07:59:10 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-2.6 1/2] [TCP]: Fix ratehalving with bidirectional
 flows

On Mon, 30 Jul 2007, David Miller wrote:

> From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Mon, 30 Jul 2007 20:18:45 +0300 (EEST)
> 
> > Actually, the ratehalving seems to work too well, as cwnd is
> > reduced on every second ACK even though the packets in flight
> > remains unchanged. Recoveries in a bidirectional flows suffer
> > quite badly because of this, both NewReno and SACK are affected.
> > 
> > After this patch, rate halving is performed for ACK only if
> > packets in flight was supposedly changed too.
> > 
> > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> 
> This fix looks great, and I see no potential problems with
> Reno after doing a bit of auditing.
> 
> Applied and I'll push to -stable too.

I think it's probably good to add tp->snd_una != prior_snd_una
check there too... It's not going to make a large difference,
mostly just to be conservative when skb collapse stuff got done
(and maybe to annoy cheaters too though I couldn't at this point
figure out how they could abuse it)...

...I think I can come up with that on Wednesday, so please hold
stable push until that.

-- 
 i.