[ofa-general] Re: [RFC] [PATCH 0/3] 2.6.22 or 23 ib: add path record cache

[Michael S. Tsirkin]

> >1. What happens on e.g. a heterogenious network? It seems that
> >path to a specific GID might change e.g. MTU without GID
> >going in/out of service. How would this be handled?

> If the path parameters change without a GID going in/out of service, then the
> cached path records would be off.  A forced cache refresh would be needed.  This
> could be done with an application (or manually) writing to the
> 'ib_local_sa/refresh' file.

A straight-forward approach would be to listen for port up/down events
rather than or in addition to GID in/out, and do network discovery by DR SMPs.

> I also looked at the path record caching
> behavior in ipoib as a starting point.

 Hmm. IPoIB by design does not handle heterogenious
 networks too well (consider problems we have selecting bcast group rate).
 MTU is also basically forced to 2K.
 So this might not have been such a great example :)

> From what I could tell, ipoib caches a
> path record per DGID, and requires bringing the device down/up to refresh the
> cache.  (Someone tell me if my understanding is off here.)

That's not entirely correct. For example, arp cache might get cleaned
by a timer, or by direct user request, or by other means.
When this happens, address handles and path records get freed.
Various IB events also trigger cache flush, such as the reregister event.

-- 
MST