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

[Shirley Ma]

On Wed, 2008-01-23 at 16:25 +0200, Dotan Barak wrote:
> What will happen if the IB port supports 4KB MTU but the operational MTU 
> of this port is bellow this value?
	Thanks for your review Dotan. The purpose to query port is for
receiving buffer allocation. First we don't need to reallocate buffer
when the IPoIB MTU changes from 2K to 4K. Second we don't want to waste
memory when the port only supports 2K MTU or less. As I said in previous
email, it's IPoIB broadcast group MTU value determined the subnet
link-MTU when the operational MTU of this port is below this value,
IPoIB broadcast group MTU will be below this value.
	Have you tested the existing IPoIB with IPoIB broadcast MTU less than
2K, like set IPoIB broadcast MTU as 1K and Chasis port as 2K? If so, do
you see any issues?
	I will test the senarios port MTU is 4K, IPoIB broadcast MTU is 2K.
	If there is any issue, it can be addressed by replacing
priv->max_ib_mtu by priv->mcmember.mtu in ipoib_ud_buf_size() when
broadcast group is presented.

Thanks
Shirley