netdev - Re: [PATCH v7] rps: Receive Packet Steering

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Message-ID: <1268809673.2932.62.camel@edumazet-laptop>
Date:	Wed, 17 Mar 2010 08:07:53 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH v7] rps: Receive Packet Steering

Le mercredi 17 mars 2010 à 09:54 +0800, Changli Gao a écrit :
> On Wed, Mar 17, 2010 at 5:13 AM, David Miller <davem@...emloft.net> wrote:
> >
> > I'll integrate this as soon as I open up net-next-2.6
> 
> It is really a good news. Now linux also can dispatch packets as
> FreeBSD does via netisr. Can we walk farer, and support weighted
> distribution?
> 

May I ask why ? What would be the goal ?

If you perform too much work behalf the first cpu (the one actually
dealing with the device and dispatching packets to other cpus), you risk
bringing into its cache whole packet and consuming too many cpu cycles.

For instance, I would prefer a basic spreading, and try to reorganise
sk_buffs to that this cpu touches only one cache line in sk_buff, and
read one cache line in packet data to compute rxhash.

Then some NIC could compute rxhash themselves and provide it in their
rx_desc. Of course multiqueue support is much better and current
hardware prefer to implement the real thing.

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