Re: Alignment of skb->data (Mylex lne390 on jensen-boards)

Alan Cox (
Fri, 31 Jul 1998 10:38:35 +0100 (BST)

> At the moment I am trying to fix the most important protocol-entities of the
> tcp/ip-stack (arp and ip run, now I am messing with icmp) so that they produce
> skb->data aligned on 16-byte boundaries ...

They already generally do land the IP header on a 16 byte boundary. Thats
normally more productive than misaligning the IP header to align the MAC

> However, would it be possible in future terms to establish an
> alignment-standard for the skb->data pointer before it is handed to the
> block_output method? It would not only make my Mylex run, but an aligned

The Linux approach for both incoming and outgoing buffers is to try and
align the IP header within the stack on a 16 byte boundary. That gives
the best stack performance with good cards.

> Does the operation at the and ensure a 16-byte alignment? I have removed them

It ensures 16 byte alignment of the IP/TCP/UDP etc headers and for most
cases also 4 byte alignment of the data payload. Unfortunately an ethernet
header is a poor length. 8(


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