netdev - Re: ip_summed setting for TCP pure-ACK packets

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Message-ID: <1289320126.2774.17.camel@edumazet-laptop>
Date:	Tue, 09 Nov 2010 17:28:46 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>,
	sf-linux-drivers <linux-net-drivers@...arflare.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: ip_summed setting for TCP pure-ACK packets

Le mardi 09 novembre 2010 à 16:24 +0000, Ben Hutchings a écrit :
> On Mon, 2010-11-08 at 17:56 +0100, Eric Dumazet wrote: 
> > Le lundi 08 novembre 2010 à 16:35 +0000, Ben Hutchings a écrit :
> > > As we discussed at LPC:
> > > 
> > > Current controllers handled by the sfc driver have a per-queue (rather
> > > than per-packet) option for checksum generation.  Currently pure-ACK
> > > packets sent by TCP have ip_summed == CHECKSUM_NONE and we must send
> > > them on hardware queues with checksum generation disabled.  To support
> > > this, we allocate 2 hardware queues per core TX queue.
> > > 
> > > To reduce the risk of reordering (and possibly the number of hardware TX
> > > queues required), it would be helpful for TCP to set ip_summed ==
> > > CHECKSUM_PARTIAL on pure-ACK packets when the output device is known to
> > > support checksum generation.
> > > 
> > > Ben.
> > > 
> > 
> > Hmm
> > 
> > Do you mean commit 2e8e18ef52e7dd1af0a3bd1 is not enough ?
> 
> It might well be... I must admit I hadn't thought to check whether this
> issue had gone away.
> 
> Yes, that does the trick.  Sorry for wasting people's time on this.
> 

You're welcome ;)



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