[openib-general] [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K

[Michael S. Tsirkin]

Quoting r. Hal Rosenstock <halr at voltaire.com>:
> Subject: Re: [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K
> 
> On Wed, 2006-09-13 at 17:49, Michael S. Tsirkin wrote:
> > Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > Subject: Re: [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K
> > > 
> > > On Wed, 2006-09-13 at 17:09, Michael S. Tsirkin wrote:
> > > > Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > > > Subject: Re: [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K
> > > > > 
> > > > > On Wed, 2006-09-13 at 15:05, Michael S. Tsirkin wrote:
> > > > > > Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > > > > > > If I understood Michael's comment properly, this will have the side
> > > > > > > > effect that IPoIB won't work since IPoIB requires 2K MTUs.  As far as
> > > > > > > > I know, there is no way to specify whether a path is needed for UD vs.
> > > > > > > > RC in the path query.
> > > > > > > 
> > > > > > > I don't know how either. I don't think it can be done (at least
> > > > > > > currently per the standard).
> > > > > > 
> > > > > > We don't really need to know whether path is for RC or UD QP.
> > > > > > IPoIB needs MTU >= 2K so it should set mtu selector to >= 2K.
> > > > > 
> > > > > That's the default and not the minimum MTU (for IPoIB).
> > > > 
> > > > How isn't it?
> > > 
> > > Look at RFC 4391 as to the requirement.
> > 
> > I'm talking about our implementation not the spec.
> 
> Don't we risk interop issues by relying on things not required in the
> spec ?

Yo confuse me. IPoIB currently assumes that
broadcast group MTU <= path MTU
for any path, but does not set MTU selector in SA query
so SA could thinkably give it any MTU.

This is assumption not in the spec and I think should be fixed ASAP,
by setting path selector.


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MST