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

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Message-ID: <Pine.LNX.4.64.0907251443170.25573@ask.diku.dk>
Date:	Sat, 25 Jul 2009 14:45:03 +0200 (CEST)
From:	Jesper Dangaard Brouer <hawk@...u.dk>
To:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
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, 24 Jul 2009, Peter P Waskiewicz Jr wrote:

> 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.

Well, thats great, as it will suit me better, as our multicast addresses 
are nicely grouped :-)

Hilsen
   Jesper Brouer

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