Dropping NETIF_F_SG since no checksum feature.

Michael S. Tsirkin
2006-10-09T17:47:24Z

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