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

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Message-ID: <1383106577.4857.30.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Tue, 29 Oct 2013 21:16:17 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, christoph.paasch@...ouvain.be,
	netdev@...r.kernel.org, hkchu@...gle.com, mwdalton@...gle.com
Subject: Re: [PATCH v2 net-next] net: introduce gro_frag_list_enable sysctl

On Wed, 2013-10-30 at 12:08 +0800, Herbert Xu wrote:
> On Tue, Oct 29, 2013 at 09:06:52PM -0700, Eric Dumazet wrote:
> >
> > I am not sure 64K GRO packets that must be segmented are going to be
> > faster than 22K packets without segmentation at all (TSO path on xmit)
> 
> Indeed that is a tough call, but I think conceptually the 64K
> case is much nicer than a sysctl that gets magically turned off.

The thing is this only matters for hosts receiving at line rate on few
TCP flows.

A router should not build too big GRO packets, as it adds latencies.

Really, we had to make TSO packets being auto sized, lets not add the
syndrome again.

So I do not really understand David concern about emitting a warning.

If a machine is used as a router, building GRO packets of 17 MSS is
absolutely fine.


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