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Date: Mon, 08 Oct 2007 00:04:51 -0700 (PDT) From: David Miller <davem@...emloft.net> To: shemminger@...ux-foundation.org Cc: netdev@...r.kernel.org Subject: Re: [RFC net-2.6.24] skbuff: change skb_frag_struct to scatterlist From: Stephen Hemminger <shemminger@...ux-foundation.org> Date: Fri, 5 Oct 2007 17:43:22 -0700 > Replace the skb frag list with the common scatterlist definition. > This allows device drivers to use dma_scatter/gather operations which > may be faster on some platforms. As a side benefit, it is easier to > handle dma mapping error unwind. > > This idea came up long ago, just never got implemented. > Reimplemented against net-2.6.24. This version is for comment, not > tested yet. > > Signed-off-by: Stephen Hemminger <shemminger@...ux-foundation.org> Thanks for keeping this idea alive. But this isn't the hard part. The issue is that skb->data is still seperate, and as long as that's true DMA mapping error recovery is still a complete mess because we still have to do two seperate DMA mappings on transmit, one of which is conditional, instead of one call which is easy to handle properly. We could do something cute like have the packet building routines use skb_shinfo(skb)->frags[1] and onward, and then right before ->hard_start_xmit() we fill in skb_shinfo(skb)->frags[0] with virt_to_page(skb->data) etc. No page refcount bumps on this magic first entry, in order for it to be as near zero cost as possible. Anyways, just one idea. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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