netdev - Re: [RFC net-next PATCH V1 0/9] net: fragmentation performance scalability on NUMA/SMP systems

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Date:	Mon, 26 Nov 2012 07:15:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Thomas Graf <tgraf@...g.ch>, Cong Wang <amwang@...hat.com>,
	Patrick McHardy <kaber@...sh.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [RFC net-next PATCH V1 0/9] net: fragmentation performance
 scalability on NUMA/SMP systems

On Mon, 2012-11-26 at 15:42 +0100, Jesper Dangaard Brouer wrote:
> On Sun, 2012-11-25 at 08:11 -0800, Eric Dumazet wrote:
> > On Sun, 2012-11-25 at 09:53 +0100, Jesper Dangaard Brouer wrote:
> > 
> > > Yes, for the default large 64k packets size, its just a "fake"
> > > benchmark.  And notice with my fixes, we are even faster than the
> > > none-frag/single-UDP packet case... but its because we are getting a
> > > GSO/GRO effect.
> > 
> > Could you elaborate on this GSO/GRO effect ?
> 
> On the big system, I saw none-frag UDP (1472 bytes) throughput of:
>   7356.57 + 7351.78 + 7330.60 + 7269.26 = 29308.21 Mbit/s
> 
> While with UDP fragments size 65507 bytes I saw:
>   9228.75 + 9207.81 + 9615.83 + 9615.87 = 37668.26 Mbit/s
> 
> Fragmented UDP is faster by:
>  37668.26 - 29308.21 = 8360.05 Mbit/s
> 
> The 65507 bytes UDP size is just a benchmark test, and have no real-life
> relevance.  As performance starts to drop (below none-frag/normal case)
> when the frag size is decreased, to more realistic sizes...

Yes, but I doubt GRO / GSO are the reason you get better performance.

GRO doesnt aggregate UDP frames.




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