netdev - Re: [PATCH][net-next] LRO: improve aggregation in case of zero TSecr packets

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Message-Id: <200908312015.18470.opurdila@ixiacom.com>
Date:	Mon, 31 Aug 2009 20:15:18 +0300
From:	Octavian Purdila <opurdila@...acom.com>
To:	David Miller <davem@...emloft.net>
Cc:	themann@...ibm.com, raisch@...ibm.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH][net-next] LRO: improve aggregation in case of zero TSecr packets

On Monday 31 August 2009 08:11:05 David Miller wrote:

> From: Octavian Purdila <opurdila@...acom.com>
> Date: Thu, 27 Aug 2009 02:08:31 +0300
>
> > This fixes a temporary performance issue we noticed in back to back
> > TSO - LRO tests when such tests are run within five minutes after
> > boot.
> >
> > The TSval field of TCP packets is filled in based on the current
> > jiffie, which is initialized at -300*HZ. That means that in 5 minutes
> > after reboot it will wrap to zero.
>
> RFC1323 says we absolutely must ignore zero TSecr values.
>
> It is a bug that the stack emits a zero value when it means to give a
> real TSecr value that will be used.
>
> Probably we can do something like emit '1' when we would emit '0'
> based upon jiffies.
>
> And this would be an improvement from now in that having a off-by-one
> TSecr in this situation is better than emitting one which we can
> guarentee will be ignored.

Right, why did I thought that the LRO TSecr issue can happen even when 
emitting a right TSval ? :-/

I'll follow with a patch which takes this approach.

Thanks,
tavi
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