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

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Date:	Fri, 13 Nov 2009 14:55:50 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
CC:	Jarek Poplawski <jarkao2@...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

Changli Gao a écrit :

> 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.

Yes, but redo your test with normal load (including several user threads
fighting for scheduler/cpu use) :)

softirq preempts user threads instantly (they are interrupts after all :) ),
while workqueue do compete with other workqueues/threads.

Tom Herbert RPS solution is still using softirqs.

I like to test workqueue based solution with IFB, but some people might still
keep previous pure softirq solution for production environment, not benchmarks...

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