Felix Marti wrote:
-----Original Message-----
From: Tom Tucker [mailto:[EMAIL PROTECTED]
Sent: Tuesday, October 23, 2007 9:32 PM
To: Felix Marti
Cc: Kanevsky, Arkady; Glenn Grundstrom; Sean Hefty; Steve Wise; Roland
Dreier; [EMAIL PROTECTED]; OpenFabrics General
Subject: Re: [ofa-general] [RFP] support for iWARP requirement -
activeconnectside MUST send first FPDU
Felix Marti wrote:
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:general-
[EMAIL PROTECTED] On Behalf Of Kanevsky, Arkady
Sent: Tuesday, October 23, 2007 6:26 PM
To: Glenn Grundstrom; Sean Hefty; Steve Wise
Cc: Roland Dreier; [EMAIL PROTECTED]; OpenFabrics
General
Subject: RE: [ofa-general] [RFP] support for iWARP requirement -
activeconnectside MUST send first FPDU
This is still a protocol and should be defined by IETF not OFA.
But if we get agreement from all iWARP vendors this will be a good
step.
[felix] This will not work with a Chelsio RNIC which follows the
IETF
specification by a) not issuing a 0B RDMA Write to the wire and b)
silently consuming an incoming 0B write. Therefore 0B RDMA Writes
cannot
be 'abused' for such a synchronization mechanism. I believe that the
mentioned apps adhering to the iWarp requirement do a 'send' from
the
active side and only have the passive side issue RDMA ops once the
incoming send has been received. I would guess that following a
similar
model is the best way to go and supported by all iWarp vendors
implementing the IETF spec.
IMO, the iWARP vendors _must_ get together and work on MPA '2'.
Standardizing FPDU 'abuse' might be a good place to start, but it
needs
to be fixed to support peer-to-peer going forward.
In the mean-time, imperfectly hiding the issue in the Firmware, uDAPL,
the iWARP CM or anywhere else except the application seems to me to be
the only customer friendly solution.
[felix] While I'm not against trying to hide the connection migration
details somewhere below the ULP, I'm not convinced that the issue is as
severe as you make it to be and I would not press to have the issue
resolved in a matter that requires a new MPA version. In fact, the
different rdma transports (and maybe even different versions of the same
transport (in the case of IB)) provide different features and I would
assume that ULPs will eventually code to these features and must thus be
aware of the underlying transport protocol. In that bigger picture, the
connection migration issue at hand seems fairly trivial to solve even if
it requires an ULP change...
I didn't make an argument about severity. Qualifying the severity is in
the customer's purview. I'm simply pointing out the following: a) the
perspective that the restriction is trivial is how we got here, b)
making the app change is putting a decision in the customer's hands that
IMO an iWARP vendor would rather they didn't have to make "Do I or don't
I support iWARP?", and c) you have the power to hide this behavior for
most cases.
Finally, I believe RFC means "Request for Comment". Well here's one last
comment -- "Add an FPDU message at the end of MPA exchange and fix the
problem in the protocol."
If we can not get agreement on it on reflector lets do
it at SC'07 OFA dev. conference.
Arkady Kanevsky email: [EMAIL PROTECTED]
Network Appliance Inc. phone: 781-768-5395
1601 Trapelo Rd. - Suite 16. Fax: 781-895-1195
Waltham, MA 02451 central phone: 781-768-5300
-----Original Message-----
From: Glenn Grundstrom [mailto:[EMAIL PROTECTED]
Sent: Tuesday, October 23, 2007 9:02 PM
To: Sean Hefty; Steve Wise
Cc: Roland Dreier; [EMAIL PROTECTED];
OpenFabrics General
Subject: RE: [ofa-general] [RFP] support for iWARP
requirement - activeconnect side MUST send first FPDU
That is what I've been trying to push. Both MVAPICH2 and
OMPI have been
open to adjusting their transports to adhere to this
requirement.
I wouldn't mind implementing something to enforce this in
the IWCM or
the iWARP drivers IF there was a clean way to do it. So
far there
hasn't been a clean way proposed.
Why can't either uDAPL or iW CM always do a send from the active
to
passive side that gets stripped off? From the active side,
the first
send is always posted before any user sends, and if
necessary, a user
send can be queued by software to avoid a QP/CQ overrun. The
completion can simply be eaten by software. On the passive
side, you
have a similar process for receiving the data.
This is similar to an option in the NetEffect driver. A zero
byte RDMA write is sent from the active side and accounted
for on the passive side. This can be turned on and off by
compile and module options for compatibility.
I second Sean's question - why can't uDAPL or the iw_cm do this?
(Yes this adds wire protocol, which requires both sides to
support
it.)
- Sean
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