netdev - Re: [PATCH v2 net-next] net: introduce gro_frag_list

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Message-Id: <20131030.151225.1564115611396752473.davem@davemloft.net>
Date:	Wed, 30 Oct 2013 15:12:25 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hkchu@...gle.com
Cc:	herbert@...dor.apana.org.au, eric.dumazet@...il.com,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	mwdalton@...gle.com
Subject: Re: [PATCH v2 net-next] net: introduce gro_frag_list_enable sysctl

From: Jerry Chu <hkchu@...gle.com>
Date: Wed, 30 Oct 2013 10:39:00 -0700

> Not sure I agree - there are two different "forwarding" cases - forwarding
> to another physical NIC (to go out to the wire hence need to do GSO),
> and (for virtualization) forwarding to a virtual NIC and consumed internally
> (e.g., VM). For the latter we should strive to push GSO pkts all the way
> to the VM stack w/o breaking them up. So for virtualization GRO is all
> goodness but not sure about the regular forwarding path. (From the
> perf perspective it boils down to if the cost of GSO/GRO will offset
> the benefit of GRO. Sure if one manages to get the cost close to zero
> than there is not reason to leave GRO always on. But it's still a big if for
> now.)

More precisely, for the regular forwarding path it only needs to be
cheaper than N * cost routing lookup, where N is the number of real
packets contained in the GRO SKB.
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