netdev - Re: gso: Attempt to handle mega-GRO packets

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Date:	Thu, 7 Nov 2013 07:56:33 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com,
	Jason Wang <jasowang@...hat.com>
Subject: Re: gso: Attempt to handle mega-GRO packets

On Wed, Nov 06, 2013 at 06:02:38PM -0800, Eric Dumazet wrote:
> On Thu, 2013-11-07 at 09:47 +0800, Herbert Xu wrote:
> 
> > Say the system is fragmented sufficiently that you'll end up with
> > 0-order pages.  In that case you'll only ever be able to coalesce
> > two packets.
> 
> 4K page will contain 2 frags and they will coalesce.
> 
> Performance will still be quite good.
> 
> We probably add a tweak, to not have any hole in this case.
> 
> > 
> > Real systems that run for more than a day do end up with seriously
> > fragmented memory.
> 
> Sure, but having shallow skbs in the first place help quite a bit.
> 
> There is no perfect solution, unless of course you change virtio_net to
> provide different queues, with different frag sizes.
> 
> Sort of what NIU driver uses.
> 

I considered doing this but won't this mean packets can get reordered?
In practice we need to maintain ordering of RX frames within
a given flow, correct?

-- 
MST
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