netdev - Re: [PATCH net-next 0/4] net: cleanup for UDP tunnel's GRO

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Message-ID: <20160709181816.1f601239@halley>
Date:	Sat, 9 Jul 2016 18:18:16 +0300
From:	Shmulik Ladkani <shmulik.ladkani@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Jiri Benc <jbenc@...hat.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jesse Gross <jesse@...nel.org>,
	Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH net-next 0/4] net: cleanup for UDP tunnel's GRO

On Fri, 8 Jul 2016 19:04:27 -0400 Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:
> >> I really do wonder if GRO on top of fragmentation does have any effect.
> >> Would be great if someone has data for that already?  
> > 
> > I think that logic is kind of backwards.  It is already there.
> > Instead of asking people to prove that this change is invalid the onus
> > should be on the submitter to prove the change causes no harm.  
> 
> Of course, sorry, I didn't want to make the impression others should do
> that. I asked because Shmulik made the impression on me he had
> experience with GRO+fragmentation on vxlan and/or geneve and could
> provide some data, maybe even just anecdotal.

Few anecdotal updates.

I don't have ready-made data as the systems are not using this exact
kind of of setup.

However, by performing some quick experimentations, it reveals that GRO
on top of the tunnels, where tunnel datagrams are fragmented, has some
effect. The packets indeed get aggregated, although not aggresively as
in the non-fragmented case.

Whether the effect is significant depends on the system.

In a system that is very sensitive to non-aggregated skbs (due to a cpu
bottleneck during further processing of the decapsulated packets), the
effect of aggregation is indeed significant.

Regards,
Shmulik