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

[Hal Rosenstock]

On Wed, 2006-09-13 at 12:22, Michael S. Tsirkin 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.

But it only needs the MTU on each local side (once for the REQ and on
the remote side for the REP). It would mean that if the local side were
capable of larger MTU and the remote side were Tavor, that the REQ would
be REJ with MTU too large and need to be retried at a smaller MTU.

> However
> 1. Even opensm does not implement this optimization yet

What optimization ? I don't understand what you are saying OpenSM
doesn't support.

> 2. We need to work with existing SMs too

Not sure what the SA issue is here.

-- Hal