[ofa-general] [PATCH] IPoIB UD 4K MTU support

[Shirley Ma]

> However I came up with a tricky approach that might work well.  We
> would use two-element scatter lists for the receives, and post a
> 40-byte dummy buffer first and then a 4096 byte buffer for the actual
> packet.  Since the only thing we do with the first 40 bytes is throw
> them away, we wouldn't even have to make the 40 bytes part of the skb;
> in fact we could have one buffer that every receive uses and never
> even touch the first entry of the scatter list after initialization.
> It would even save the skb_pull(skb, IB_GRH_BYTES); we currently do
> after receiving messages.
> 
> What do you think?

I thought the same thing before for one buffer allocation, I had a
little bit concern about whether IB_GRH could be used later. I have done
scatter-gather list patch already. It's based on the PAGE_SIZE whether
to use one buffer or two buffer, similar as IPoIB-CM S/G code. It's
under testing. The only thing I haven't finished is making S/G code more
generica and merge IPoIB-CM S/G and IPoIB-UD S/G buffer allocation
togather. Since IBM eHCA does support 4K MTU and we would like our
customer to use this feature in OFED-1.3 release. If I merge the
IPoIB-CM S/G code and IPoIB-UD S/G code, it would take much longer for
testing. I wonder whether it's OK to push IPoIB-UD S/G first then merge
IPoIB-UD and IPoIB-CM later.

thanks
Shirley