netdev - Re: rps perfomance WAS(Re: rps: question

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Message-ID: <1271275130.16881.1749.camel@edumazet-laptop>
Date:	Wed, 14 Apr 2010 21:58:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	hadi@...erus.ca, Tom Herbert <therbert@...gle.com>,
	netdev@...r.kernel.org, robert@...julf.net,
	David Miller <davem@...emloft.net>,
	Changli Gao <xiaosuo@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: rps perfomance WAS(Re: rps: question

Le mercredi 14 avril 2010 à 12:44 -0700, Stephen Hemminger a écrit :
> On Wed, 14 Apr 2010 14:53:42 -0400
> jamal <hadi@...erus.ca> wrote:
> 
> > Agreed. So to enumerate, the benefits come in if:
> > a) you have many processors
> > b) you have single-queue nic
> > c) at sub-threshold traffic you dont care about a little latency
> 
> There probably needs to be better autotuning for this, there is no reason
> that RPS to be steering packets unless the queue is getting backed up.
> Some kind of high / low water mark mechanism is needed.
> 
> RPS might also interact with the core turbo boost functionality on Intel chips.
> Newer chips will make a single core faster if other core can be kept idle.
> 
> 

This was discussed a while ago, and Out Of Order packet delivery was the
thing that frightened us a bit.

Every time we change RPS to be on or off, we might have some extra
noise. Maybe we already have this problem with irqbalance ?



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