netdev - RE: [PATCH 2.6.28 3/4] myri10ge: Add Toeplitz-hashing related routines

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Date:	Fri, 12 Sep 2008 15:32:26 -0700
From:	"Duyck, Alexander H" <alexander.h.duyck@...el.com>
To:	Brice Goglin <brice@...i.com>, Jeff Garzik <jeff@...zik.org>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 2.6.28 3/4] myri10ge: Add Toeplitz-hashing related
 routines

Brice Goglin wrote:
> myri10ge uses a Toeplitz hashing. Add the corresponding select_queue()
> method without using it yet.
>
> Signed-off-by: Brice Goglin <brice@...i.com>
> ---
...
> +       /*
> +        * Note hashing order is reversed from how it is done
> +        * in the NIC, so as to generate the same hash value
> +        * for the connection to try to keep connections CPU local
> +        */
Have you given this any consideration in terms of routing performance?  It
seems to me that if you didn't reorder things you should be able to generate
the same exact hash value that you would have received on the receive side.
The end result being that packets received on queue 1 would transmit on queue
1, thus saving you a lot of cross queue thrash when routing.  Of course this
all relies on the rss_key being global and shared between ports.

Alex
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