netdev - Re: [PATCH] ifb: add multi-queue support

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Date:	Fri, 13 Nov 2009 09:18:25 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	Patrick McHardy <kaber@...sh.net>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] ifb: add multi-queue support

On Fri, Nov 13, 2009 at 04:54:50PM +0800, Changli Gao wrote:
> On Fri, Nov 13, 2009 at 3:45 PM, Jarek Poplawski <jarkao2@...il.com> wrote:
> > On 13-11-2009 07:16, Changli Gao wrote:
> >
> > I don't think so. There would be a lot of code duplication and later
> > maintenance problems only because of the scheduling method. The main
> > question is to establish if there is really no performance difference
> > (which I doubt) - unless Changli can show some tests for various
> > setups now. On the other hand, if there is a difference, why keep
> > ineffective solution - similar thing should be possible to do in the
> > softirq context as well.
> >
> > So it should not be a big problem to do it a bit messy for some
> > testing time. Since we can use separate ->ndo_start_xmit() etc. it
> > shouldn't be too messy, I guess.
> >
> 
> I have done a simple test. I run a simple program on computer A, which
> sends SYN packets with random source ports to Computer B's 80 port (No
> socket listens on that port, so tcp reset packets will be sent) in
> 90kpps. On computer B, I redirect the traffic to IFB. At the same
> time, I ping from B to A to get the RTT between them. I can't see any
> difference between the original IFB and my MQ version. They are both:
> 
> CPU idle: 50%
> Latency: 0.3-0.4ms, burst 2ms.
> 

I'm mostly concerned with routers doing forwarding with 1Gb or 10Gb
NICs (including multiqueue). Alas/happily I don't have such a problem,
but can't help you with testing either.

Regards,
Jarek P.
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