netdev - Re: Single packet receiving in multiple ring buffers

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Message-Id: <20080522.115755.202204829.davem@davemloft.net>
Date:	Thu, 22 May 2008 11:57:55 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	johnpol@....mipt.ru
Cc:	kchudgar@...c.com, kchudgar.linux@...il.com, netdev@...r.kernel.org
Subject: Re: Single packet receiving in multiple ring buffers

From: Evgeniy Polyakov <johnpol@....mipt.ru>
Date: Thu, 22 May 2008 22:49:07 +0400

> You have to copy part of the data (up to and including transport headers)
> into skb->data.

You don't necessarily have to.  The input paths of the networking
stack will pull into the skb->data, as needed, using
pskb_may_pull() calls.

I did some tests with the NIU driver on receive, and to be
honest there was nearly zero performance gain from pre-copying
into skb->data from the paged SKB area preemptively before
passing the packet in via netif_receive_skb().
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