[openib-general] Re: [mgtwg] [OpenSM] multicast group - mtu_selector question

[Greg Pfister]

Hi, Yael.

My understanding is that your understanding is almost correct, with two 
adjustments -- one technical, one formal, from the point of view of the 
IBA spec.

MtuSelector does have meaning  in queries, not just in the scope of 
creation. E.g.,if you query using 1 and 1024 (less than 1024), and the 
only group existing that otherwise matches has an MTU of 2048, you will 
not find <any members of> that group.

Formal: The statement "mcgroup does not carry the mtu_selector value" is 
meaningless from the spec's position. It is silent (purposely) on any 
implementation, hence is silent about what may be in any data structure 
created to represent a multicast group.  Naturally, an OpenIB 
implementation can't take that position.

Personal opinion, not spec: The query exception above doesn't change the 
fact that it looks less than useful to maintain the selector in the 
mcgroup data structure.

Any comments by others?

(I'm not on the OpenIB reflector, so this may not be reflected there. If 
someone who is wants to forward this there, please feel free.)

Greg Pfister
IBM Distinguished Engineer, Member IBM Academy of Technology
IBM Systems & Technology Group, Server Technology & Architecture
(512) 838-8338 | IBM tieline 678-8338 | FAX (512) 838-3418
Sic Crustulum Frangitur

Yael Kalka <yael at mellanox.co.il> wrote on 08/08/2005 02:39:36 AM:

> Hello All,
> 
> I have a question regarding the exact meaning of the mtu selector in
> the MCMemberRecord:
> Does the multicast group carry a range of mtus according to the 
> creation request mtu_selector and
> mtu, or does it carry an exact mtu selected according to the request
> mtu_selector and mtu?
> 
> When a multicast group is created, if the value of the mtu selector 
> in the request MCMemberRecord
> is not 2 (meaning: greater than or lower than), does this value of 
> the mtu_selector have a 
> meaning outside the scope of the creation request? 
> For example, if a request to create was received with mtu selector =
> 0, and the mtu = 256.
> and the multicast group was created with the specific mtu value 2048
> (selected by the SA according to p913 l14-16):
> 1. Does a join request with mtu=1024, and selector=2 succeed?
> 2. Does a query request with mtu=256, and selector=0 (both compmask 
> are set) return the above mcgroup?
> 
> My understanding is:
> mcgroup does not carry the mtu_selector value, meaning it will 
> always carry an exact mtu value.
> Thus the answers to the previous questions are: 
> 1. No. Since the mcgroup was created with mtu=2048.
> 2. No. There is no meaning for this query (the mtu must be provided 
> along with mtu selector).
> 
> Thank you in advance,
> Yael
> 
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