netdev - Re: [PATCH] NET: Multiqueue network device support.

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Date:	Tue, 12 Jun 2007 17:47:53 -0400
From:	Jason Lunz <lunz@...ooley.org>
To:	David Miller <davem@...emloft.net>
Cc:	greearb@...delatech.com, jeff@...zik.org, netdev@...r.kernel.org,
	kaber@...sh.net, hadi@...erus.ca, peter.p.waskiewicz.jr@...el.com,
	auke-jan.h.kok@...el.com
Subject: Re: [PATCH] NET: Multiqueue network device support.

On Tue, Jun 12, 2007 at 02:26:58PM -0700, David Miller wrote:
> The MAC is still very much centralized in most designs.
> 
> So one way they'll do it is to support assigning N MAC addresses,
> and you configure the input filters of the chip to push packets
> for each MAC to the proper receive queue.
> 
> So the MAC will accept any of those in the N MAC addresses as
> it's own, then you use the filtering facilities to steer
> frames to the correct RX queue.
> 
> The TX and RX queues can be so isolated as to be able to be exported
> to virtualization nodes.  You can give them full access to the DMA
> queues and assosciated mailboxes.  So instead of all of this bogus
> virtualized device overhead, you just give the guest access to the
> real device.
> 
> So you can use multiple queues either for better single node SMP
> performance, or better virtualization performance.

Are you aware of any hardware designs that allow other ways to map
packets onto rx queues?  I can think of several scenarios where it could
be advantageous to map packets by IP 3- or 5-tuple to get cpu locality
all the way up the stack on a flow-by-flow basis. But doing this would
require some way to request this mapping from the hardware.

In the extreme case it would be cool if it were possible to push a
bpf-like classifier down into the hardware to allow arbitrary kinds of
flow distribution.

Jason
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