From:
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Krause
Sent: Friday, October 01, 2004
1:29 AM
To: [EMAIL PROTECTED]
Subject: Re: Fwd: Re:
[openib-general] static LID computationwithTS_HOST_DRIVER
At 03:40 PM 9/30/2004, David M. Brean wrote:
The IBA provides two mechanisms for updating subnet management data:
1) through the verbs - see Modify HCA (section 11.2.1.3)
2) through Subnet management packets (SMPs) - see Subnet Management
Class (section 14.2)
The IBA only supports updating the LID via SMPs (#2 above) and an entity
using SMPs must have the M_Key. If that entity doesn't have the M_Key,
then it can't reliably change the LID.
In addition, the IBA allows an endnode to request, through the verbs
interface provided for the "node reinitialization" (see 14.4.4)
mechanism, that subnet management state, such as the LID, be preserved, when a
port transitions through the DOWN state. However, the SM may not honor
that request so the endnode must handle that possibility because LID assignment
policy is owned by the SM. Furthermore, this mechanism is used on ports
that have previously been initialized by the SM (maybe that's why it's called
the reinitialization function :)).
Given the mechanisms in the specification, I think that its possible to have IB
clients use loopback, even under the endnode power-up scenario, while the port
is not in the ACTIVE state and have them continue without disruption when the
port is made ACTIVE on the subnet by the SM with use of the reinitialization
mechanism. This is a very useful mechanism for various failover
situations.
This is a reasonable approach where the loopback LID being used is updated upon
the port being initialized (akin to solving this in the CI but still allowing
CM to work with a known LID. It avoids any complexity in the SM having to
preserve LID that may not be optimal or potentially unique within the
subnet.
Not sure this might work but it seems to me that APM mech could be used to
configure a new configured LID and then transfer the connection to the
configured. May take a bit of work in CM as APM is nominally set up
during these exchanges.
There is no current IBA mechanism or protocol for an endnode to set
just the LID, even if it had the M_Key, and have the SM preserve that value.
Agreed.
Mike
-David
Roland Dreier wrote:
I don't see anything in the spec that forbids a CA from having an
arbitrary value in PortInfo:LID after initialization but before the SM
discovery (please correct me if I missed something). I also don't see
anything that forbids an SM implementation from providing a mechanism
for preserving the LIDs it finds or administratively assigning LIDs.
Of course none of this is required but I don't see a problem with
allowing it.
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