netdev - Re: [PATCH v5] rfs: Receive Flow Steering

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Date:	Fri, 16 Apr 2010 09:32:06 -0400
From:	jamal <hadi@...erus.ca>
To:	Andi Kleen <andi@...obates.de>
Cc:	Tom Herbert <therbert@...gle.com>, davem@...emloft.net,
	netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH v5] rfs: Receive Flow Steering

On Fri, 2010-04-16 at 13:57 +0200, Andi Kleen wrote:

> One thing I've been wondering while reading if this should be made
> socket or SMT aware.
> 
> If you're on a hyperthreaded system and sending a IPI
> to your core sibling, which has a completely shared cache hierarchy,
> might not be the best use of cycles.
> 
> The same could potentially true for shared L2 or shared L3 cache
> (e.g. only redirect flows between different sockets)
> 
> Have you ever considered that?
> 

How are you going to schedule the net softirq on an empty queue if you
do this?
BTW, in my tests sending an IPI to an SMT sibling or to another core
didnt make any difference in terms of latency - still 5 microsecs.
I dont have dual Nehalem where we have to cross QPI - there i suspect
it will be longer than 5 microsecs.

cheers,
jamal

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