Fwd: [RFC][PATCH 4/5] I/OAT DMA support and TCP acceleration

[Chris Leech]

Sorry, bounced from vger the first time due to formatting

---------- Forwarded message ----------
From: Chris Leech <christopher.leech@xxxxxxxxx>
Date: Dec 20, 2005 11:05 PM
Subject: Re: [RFC][PATCH 4/5] I/OAT DMA support and TCP acceleration
To: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Cc: lkml <linux-kernel@xxxxxxxxxxxxxxx>, netdev
<netdev@xxxxxxxxxxxxxxx>, "Grover, Andrew" <andrew.grover@xxxxxxxxx>,
"Ronciak, John" <john.ronciak@xxxxxxxxx>

On 12/20/05, Eric Dumazet <dada1@xxxxxxxxxxxxx> wrote:
>  Please consider not enlarging cb[] if not CONFIG_NET_DMA ?
>
> I mean, most machines wont have a compatable NIC, so why should they pay the
> price (memory, cpu) in a critical structure named sk_buff ?
>
> #ifdef CONFIG_NET_DMA
> typedef dma_cookie_t net_dma_cookie_t;
> #else
> typedef struct {} net_dma_cookie_t;
> #endif
>
> ...
>
>         char   cb[40+sizeof(net_dma_cookie_t)];
>

 That could be a good way to deal with it.  Actually, I should double
check the length of tcp_skb_cb.  I took a quick look and thought that
there might be some room left there anyway, even though the comment in
tcp.h says otherwise.

 -Chris
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