[ofa-general] OFED-1.3beta IPoIB testing questions

[Shirley Ma]

Hello Eli,

I just found my email somehow became SPAM. I just resent my comments,
hopefully it can go through.

Eli Cohen <eli at dev.mellanox.co.il> wrote on 12/02/2007 05:45:59 AM:

> On Fri, 2007-11-30 at 15:28 -0800, Shirley Ma wrote:
> > I just touch tested ofed-1.3 beta IPoIB. And found there was a kernel
> > parameter hw_csum being added in IPoIB. I have several questions here:
> > 1. Why not using ethtool to set up these HW_CSUM flags?
> There is no adequate interface in Ethtool for doing it so we use a
> module parameter. This is because we see this as a static configuration
> per host.

Ethtool does support rx csum and tx csum:
#define ETHTOOL_GRXCSUM  0x00000014 Get RX hw csum enable (ethtool_value)
#define ETHTOOL_SRXCSUM  0x00000015 Set RX hw csum enable (ethtool_value)
#define ETHTOOL_GTXCSUM  0x00000016 Get TX hw csum enable (ethtool_value)
#define ETHTOOL_STXCSUM  0x00000017 /* Set TX hw csum enable
(ethtool_value)

We should use ethtool here.

> > 2. I haven't looked at the detailed code yet, is that possible with
this
> > flag, TCP/IP will not do CSUM for HCA which has no TCP/IP offload
support?
> Yes, the HCA need not have checksum offload support. the idea is the IB
> ICRC provides the insurance that the packets are not corrupt.

That's something we discussed long time ago when we wanted GSO to avoid
extra copy by using ICRC to enable SG feature. I remembered Roland rejected
this idea since there could be potenical data corruption. And even if we do
prove that ICRC is 100% accurate, then we should have some codes here to
limit the IP destination within IB subnet when using ICRC. Otherwise, if
the packets routing out to ehthernet IP subnet, these packets will be
dropped.

Thanks
Shirley
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