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

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Message-ID: <CAPshTCgykFMa=4rnQ3TKa2cfgWYj4TgByO2GbzLzq71Y_=oc=Q@mail.gmail.com>
Date:	Tue, 29 Oct 2013 19:13:50 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Christoph Paasch <christoph.paasch@...ouvain.be>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Michael Dalton <mwdalton@...gle.com>
Subject: Re: [PATCH v2 net-next] net: introduce gro_frag_list_enable sysctl

On Tue, Oct 29, 2013 at 7:05 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Tue, Oct 29, 2013 at 10:02:53PM -0400, David Miller wrote:
>> From: Eric Dumazet <eric.dumazet@...il.com>
>> Date: Tue, 29 Oct 2013 17:53:48 -0700
>>
>> > So should we apply the first fix to avoid the BUG_ON() ?
>>
>> Please be more specific, are you talking about splitting up
>> this patch in some way?
>
> I think Eric is referring to the patch that removes the BUG_ON
> in skb_segment and deals with the new mega-GRO packets.
>
> I think that's fine for stable, but for the long term we should
> fix it properly as these new meag-GRO packets still retain the
> existing packet boundaries and are trivially segmentable.
>
> If we are indeed able to do that, I doubt we would even need
> the sysctl patch since the GRO performance should be vastly
> superior to the non-GRO case, even for a router/bridge.

Probably not the case for the simple forwarding case. See my
test result of some small (5-8%) CPU+throughput penalty from
GRO (over GRE tunnel) posted previously. But I can believe
the number may be very different if the forwarding path involves
more work (NAT, iptables filtering,...,etc) resulting in a higher per
pkt cost.

Best,

Jerry

>
> Cheers,
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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