netdev - Re: [PATCH v6] net: batch skb dequeueing from softnet input_pkt

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Date:	Mon, 03 May 2010 00:08:24 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Miller <davem@...emloft.net>, hadi@...erus.ca,
	xiaosuo@...il.com, therbert@...gle.com, shemminger@...tta.com,
	netdev@...r.kernel.org, lenb@...nel.org, arjan@...radead.org
Subject: Re: [PATCH v6] net: batch skb dequeueing from softnet
 input_pkt_queue

Le dimanche 02 mai 2010 à 23:54 +0200, Andi Kleen a écrit :
> On Sun, May 02, 2010 at 11:45:55PM +0200, Eric Dumazet wrote:

> > Tests just prove the reverse.
> 
> What do you mean? 
> 

Test I did this week with Jamal.

We first set a "ee" rps mask, because all NIC interrupts were handled by
CPU0, and Jamal thought like you, that not using cpu4 would give better
performance.

But using "fe" mask gave me a bonus, from ~700.000 pps to ~800.000 pps

CPU : E5450  @3.00GHz
Two quad-core cpus in the machine, tg3 NIC.

With RPS, CPU0 does not a lot of things, just talk with the NIC, bring a
few cache lines per packet and dispatch it to a slave cpu.

> HT (especially Nehalem HT) is useful for a wide range of workloads.
> Just handling network interrupts for its thread sibling is not one of them.
> 

Thats the theory, now in practice I see different results.

Of course, this might be related to hash distribution being different
and more uniform.

I should redo the test with many more flows.

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