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

[Hal Rosenstock]

On Wed, 2006-09-13 at 15:03, Michael S. Tsirkin wrote:
> Quoting r. Fabian Tillier <ftillier at silverstorm.com>:
> > Subject: Re: [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K
> > 
> > On 9/13/06, Michael S. Tsirkin <mst at mellanox.co.il> wrote:
> > > Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > > Subject: Re: [openib-general] [PATCH for-2.6.18] IB/cma: option to limitMTU to 1K
> > > >
> > > > On Wed, 2006-09-13 at 11:57, Michael S. Tsirkin wrote:
> > > > > Tavor systems get better performance with 1K MTU. Since there does
> > > > > not seem to be any way to find out whether the remote system uses Tavor,
> > > > > add an option to limit the MTU globally.
> > > >
> > > > Can't Tavor be determined locally ?
> > >
> > > It can, but we need this for remote tavor as well, anyway.
> > >
> > > > And couldn't the remote end negotiate the MTU down (if Tavor) as well ?
> > >
> > > The way to do this is would be for SA to select 1K MTU if it detects Tavor on one side
> > > and if this does not conflict with MTU selector.
> > 
> > You can't do this because the SA doesn't have a way to tell if a path
> > query is going to be used for RC or UD, and IPoIB needs paths with 2K
> > MTU.
> 
> I think we can do that without breaking IPoIB.
> IPoIB needs mtu >= 1K.

Huh ?

>  IPoIB sets mtu selector to >= 2K.

I don't think that's a requirement for IPoIB.

> I am talking about users that do not set mtu selector.

Understood.

-- Hal