netdev - Re: [RFC PATCH] [TCP]: Move clearing of the prior

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Message-ID: <Pine.LNX.4.64.0703012220300.25330@kivilampi-30.cs.helsinki.fi>
Date:	Thu, 1 Mar 2007 22:26:57 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCH] [TCP]: Move clearing of the prior_ssthresh due to
 ECE earlier

On Thu, 1 Mar 2007, Ilpo Järvinen wrote:

> Previously the prior_ssthresh was only used in the undo functions
> that were called by fastretrans_alert. FRTO processing, however,
> happens before that and one of the responses is doing undo too.
> 
> I think that after this patch, FRTO should be ECN-safe; only the
> undo_cwr response is a suspect anyway. The possible cases:
> 
[...snip...]
> 
> This problem could be solved locally in the undo_cwr response of
> FRTO by falling back to ratehalving response when FLAG_ECE is
> enabled.

I think that doing it in the response is better that this approach,
since it knows that the ssthresh has been halved already within that
round-trip, so there is no need to do that again... I'll submit the
patch tomorrow... With this prior_ssthresh clearing move alone, the 
ssthresh ends up being halved twice if I tought it right (first in 
tcp_enter_frto and then again in tcp_enter_cwr that is called from 
fastretrans_alert)... So please, drop this patch.

-- 
 i.