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

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Date:	Sat, 02 Nov 2013 11:28:27 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Oleg A.Arkhangelsky" <sysoleg@...dex.ru>
Cc:	David Miller <davem@...emloft.net>,
	"hkchu@...gle.com" <hkchu@...gle.com>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"christoph.paasch@...ouvain.be" <christoph.paasch@...ouvain.be>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"mwdalton@...gle.com" <mwdalton@...gle.com>
Subject: Re: [PATCH v2 net-next] net: introduce gro_frag_list_enable sysctl

On Sat, 2013-11-02 at 21:43 +0400, Oleg A.Arkhangelsky wrote:
> 
> 30.10.2013, 06:33, "David Miller" <davem@...emloft.net>:
> 
> > GRO should always win, even on a router, because it decreases the
> > number of fundamental operations (routing lookups) that the stack
> > needs to perform.
> 
> Yes, unless the case when you're using Linux as IP router which is
> forwarding 500K mixed IP (TCP and UDP) flows traffic @ 10-20 Gbit/s.
> Then GRO is unnecessarily overhead, cause there's no possibility to
> accumulate adequate GRO list in such scenario.
> 

This was assuming the aggregation factor was not 0.

Even with 500K flows, you can have typically bursts of two packets per
flow.

Thats one of the reason why I chose to default
/proc/sys/net/ipv4/tcp_min_tso_segs to 2



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