netdev - Re: [PATCH v2] ipv4: Early TCP socket demux.

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Date:	Wed, 20 Jun 2012 23:17:56 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, bhutchings@...arflare.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2] ipv4: Early TCP socket demux.

On Wed, 2012-06-20 at 14:04 -0700, Stephen Hemminger wrote:
> On Wed, 20 Jun 2012 14:01:21 -0700 (PDT)
> David Miller <davem@...emloft.net> wrote:
> 
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > Date: Wed, 20 Jun 2012 20:40:04 +0200
> > 
> > > If someone wants to tune its linux router, he probably already disables
> > > GRO because of various issues with too big packets.
> > > 
> > > GRO adds a significant cost to forwarding path.
> > 
> > No, Ben is right Eric.  GRO decreases the costs, because it means we
> > only need to make one forwarding/netfilter/classification decision for
> > N packets instead of 1.
> 
> GRO is also important for routers that interact with VM's.
> It helps reduce the per-packet wakeup of the guest VM's.

I spoke of mere routers, I was _not_ saying GRO is useless.

In most routers setups I used, I had to disable GRO, because 64Kbytes
packets on output path broke the tc setups (SFQ)

netfilter cost was hardly a problem, once correctly done.



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