[ofa-general] How to Interpret MTU reported by "ibv_devinfo" vs "ifconfig ib0"

[Kumar, Amit H.]

>
> The MTU reported by "ifconfig ib0" is the MTU used by the Linux
> TCP/IP network stack. The MTU reported by ibv_devinfo is the
> MTU that the hardware is capable of sending. This is limited
> to 4K by the Infiniband specification. The reason the network
> stack can have a higher MTU is that ib_ipoib is using the RC
> QP protocol to send IP messages larger than the hardware MTU.
> If you use "datagram" mode for ib_ipoib, you will see that
> the network stack MTU is limited to the hardware MTU - 4.

Thank you Ralph!!!  As far as common applications taking advantage of ib_ipoib
Does it help using RC QP with a higher MTU than the hardware MTU?

Does an Application, which uses Sockets API, by default make use of ib_ipoib,
if it is enabled ?

Is there any essential difference between IPoIB and ib_ipoib, or is it just a matter of usage ?

Thank you,
Amit

> >
> > Also Is there a document where I can read in detail about IPoIB and
> applications that benefit from them.
> > In general I understand that Socket based applications can make use
> of IPoIB for a better bandwidth, thought NOT for a better transport
> latency.
> > In short I am trying to understand the difference and advantage, for
> an Application using "Ethernet NIC" vs "InfiniBand HCA(IPoIB enabled)",
> apart from knowing that there is no advantage in terms of transport
> latency.
> >