[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 17:17, Michael S. Tsirkin wrote:
> > Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > > > If path MTU selector in path query allows MTU 1K (e.g. "best MTU")
> > > > and one of the sides is Tavor, select the best MTU that is 1K
> > > > and not the largest possible.
> > > 
> > > How would it be identified if the SA supports this ?
> > 
> > You mean, if SA ignores mtu selector?
> 
> No; I meant detect that one end of the PR request is a Tavor. Wasn't
> that part of it ?

SA can easily figure out it's talking to tavor by looking at vendor part id.

> If SA doesn't support MTU selector and ignoring MTU selector, it is not
> compliant and should be fixed.
> 
> > Then we are not worse off than we were before we set it - we get 2K MTU for
> > tavor and it works a bit slower.
> > 
> > > > If path MTU selector requires 2K MTU, return path with 2K MTU.
> > > 
> > > Also, I'm not sure that this is the required difference in the SA
> > > requests :-(
> > 
> > What do you mean?
> > Its not required, but its legal and it will give us better performance.
> 
> I mean that there is no requirement on what the IPoIB SA PR request
> looks like what you are using to differentiate from the PR requests for
> a connection setup.

Correct. But if IPoIB requires 2K MTU it must use MTU selector,
if it does not it's OK to give it a smaller MTU.

-- 
MST