netdev - Re: [PATCH v2] Receive Packet Steering

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Message-ID: <65634d660907171105s4989758ah533203d107924b6a@mail.gmail.com>
Date:	Fri, 17 Jul 2009 11:05:58 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v2] Receive Packet Steering

On Thu, Jul 16, 2009 at 7:48 PM, David Miller <davem@...emloft.net> wrote:
>
> From: Tom Herbert <therbert@...gle.com>
> Date: Tue, 14 Jul 2009 16:28:01 -0700
>
> > Using the Toeplitz hash in steering lookup has given us about 10% more
> > maximum pps (2 different NICs), and we haven't really noticed negative
> > effects because of the extra descriptor overhead-- so I'm not going to
> > give up on it too easily!
>
> Do you have any idea why?  Does Toeplitz distribute better?
> If so, that could be merely because either:
>
> 1) Our modulus avoidance scheme somehow decreases the distribution
>   features of the hash
>
> 2) The way we feed data into the hash has a similar effect
>
> It's worth checking out.

The advantage is that Toeplitz, or any reasonable device provided
hash, allows packet steering to be done without taking any cache
misses on the packet itself.  In particular, this helps with a NIC
that just provides Toeplitz hash (without multiQ),
--
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