[ofa-general] Re: [PATCH] opensm: preserve base lid routes

[Sasha Khapyorsky]

On 04:49 Thu 12 Jun     , Hal Rosenstock wrote:
> On Thu, 2008-06-12 at 14:33 +0300, Sasha Khapyorsky wrote:
> > On 03:59 Thu 12 Jun     , Hal Rosenstock wrote:
> > > 
> > > Would you elaborate on the motivation behind the requirement to
> > > maintain/preserve the base LID routing ?
> > 
> > I see couple advantages:
> > 
> > 1. Application which works on base LIDs only will not be affected by LMC
> 
> Yes; that's the obvious one.
> 
> > 2. Changing LMC on a fabric will not change routing paths (when LIDs are
> > not reassigned)
> 
> That's when LMC is reduced rather than increased.

Also when increased and LIDs are not reassigned.

> > 3. Finally it does better balancing for secondary LIDs ("port
> > offsetting")
> 
> Isn't that accomodated in the patch but separate from the base LID
> preservation ?

It is integrated in the patch - balancing for each LID starts from
its lower LID's port + 1. Not doing this would be really bad.

> Preserving/maintaining base LIDs is a policy decision and perhaps this
> should be an option with this as the default. For some balancing all
> paths might be more important that not disrupting base LID traffic.

This is the trick - by preserving base LID traffic and offsetting over
other LID ports we get better than before balancing. So right now it is
hard to me to see when proposed option would be useful. But probably it
would, I think we can add it then.

Sasha