linux-kernel - Dropping NETIF_F_SG since no checksum feature.

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Message-ID: <20061009174705.GG26849@mellanox.co.il>
Date:	Mon, 9 Oct 2006 19:47:05 +0200
From:	"Michael S. Tsirkin" <mst@...lanox.co.il>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, openib-general@...nib.org,
	Roland Dreier <rolandd@...co.com>
Subject: Dropping NETIF_F_SG since no checksum feature.

Hi!
I'm trying to build a network device driver supporting a very large MTU (around 64K)
on top of an infiniband connection, and I've hit a couple of issues I'd
appreciate some feedback on:

1. On the send side,
   I've set NETIF_F_SG, but hardware does not support checksum offloading,
   and I see "dropping NETIF_F_SG since no checksum feature" warning,
   and I seem to be getting large packets all in one chunk.
   The reason I've set NETIF_F_SG, is because I'm concerned that under real life
   stress Linux won't be able to allocate 64K of continuous memory.

   Is this concern of mine valid? I saw in-tree drivers allocating at least 8K.
   What's the best way to enable S/G on send side?
   Is checksum offloading really required for S/G?

2. On the receive side, what's the best/right way to create an skb that
   is larger than PAGE_SIZE?
   Do I allocate with alloc_page and fill in nr_frags with skb_fill_page_desc?
   Some drivers seem to fill in frag_list - which is better?
   I see than even skb_put only works properly on linear skb.
   What are the helpers legal for fragmented skb?

Suggestions would be appreciated.

Thanks,

-- 
MST
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