netdev - Re: [net-next-2.6 PATCH 06/13] igb: move all multicast addresses into multicast table array

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Date:	Fri, 24 Jul 2009 18:41:29 -0700
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	Jesper Dangaard Brouer <hawk@...u.dk>
Cc:	"Duyck, Alexander H" <alexander.h.duyck@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"gospo@...hat.com" <gospo@...hat.com>
Subject: Re: [net-next-2.6 PATCH 06/13] igb: move all multicast addresses
 into multicast table array

On Fri, 2009-07-24 at 01:57 -0700, Jesper Dangaard Brouer wrote:
> On Thu, 23 Jul 2009, Jeff Kirsher wrote:
> 
> > From: Alexander Duyck <alexander.h.duyck@...el.com>
> >
> > This patch moves all of the multicast addresses out of the free Receive
> > address registers and instead programs them all into the multicast table
> > array.  As a result the multicast filtering may not be as precise, but it
> > also greatly reduces the overhead for multicast addresses.
> 
> What do you mean by "the multicast filtering may not be as precise" ?
> 
> I'm planning to use these NICs for multicast traffic (both routing and 
> monitoring).  Is there any precausing I need to be aware of?
> 

The receive address registers, or RARs, are perfect match filters.  The
multicast table array, or MTA, contains hashed values of the multicast
addresses.  Therefore, it isn't a perfect match for the multicast
addresses anymore.  But to support a larger number of multicast
addresses, they can't be written to the RARs, since those resources are
small and are needed for MAC and unicast address filtering.

Cheers,
-PJ Waskiewicz

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