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

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Date:	Wed, 06 Nov 2013 07:01:10 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	christoph.paasch@...ouvain.be, netdev@...r.kernel.org,
	hkchu@...gle.com, mwdalton@...gle.com, mst@...hat.com
Subject: Re: gso: Attempt to handle mega-GRO packets

On Wed, 2013-11-06 at 21:12 +0800, Herbert Xu wrote:

> I take that back.  While the original patch was seriously broken,
> it has since been fixed by the coalescing patch that Jason Wang
> wrote.
> 

Patch was not 'broken', but a step into the right direction. I am very
sorry if you think otherwise.

> It's still pretty weird to be dividing page frags into 1500-byte
> chunks and then merging back up to 4K but at least it should do the
> right thing now.


Have you thought about arches having PAGE_SIZE=65536, and how bad it is
to use a full page per network frame ? It is lazy and x86 centered.

So after our patches, we now have an optimal situation, even on these
arches.

On x86, a full 64KB GSO packet will now fit in 2 (or 3) frags allocated
in 32KB pages (order-3) in fast path (ie if there is not high memory
pressure)

According to our tests, performance is better on x86, and virtio_net now
is usable on arches with PAGE_SIZE=65536



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