[ofa-general] Re: [Query] ib add path record cache

[Devesh Sharma]

On 5/17/07, Sean Hefty <mshefty at ichips.intel.com> wrote:
> > But initially this will generate a packet for each path, while sys
> > admin knows that path is there and he can hard-code the entries for
> > it. Other thing is that why Admin will care about creating such record
> > while SA is itself taking care, right?
>
> In your original message you asked about adding 'dummy entries' to the
> cache.  I agree that pre-loading the cache can be useful.  What I still
> am not understanding is the reasoning for adding 'dummy entries'.  By
> 'dummy entries', I've been assuming that these are invalid path records,
> but maybe that's not what you meant.
Ok if "dummy entries" word as such has created confusion then I am
sorry for that, But with that I mean that, those are valid path
records which Administrator knows in advance and while loading the
module, Admin is loading this info in the cache with user command.
>
> > Another point I want to know is,
> > When local_sa_cache module will be inserted? After SM comes up or
> > Before SM comes up?
>
> It can occur either way.  There is no restriction.  The cache responds
> to port up and GID in/out of service events to update itself.
Do you mean cache module will start building cache only after Port is UP?
>
> > If Its inserted before SM is coming up (I am assuming SM is running on
> > some node not on switch) then First Forced schedule_update() is
> > waisted, and for the first application presence of cache is
> > meaningless. Why not to keep cache effective right from the start?
>
> Pre-loading the cache with path records doesn't guarantee that those
> paths are usable.  If the SM has not come up, then the path records will
> be unusable until the SM configures the subnet, plus there's no
> guarantee that the remote endpoints specified by the paths are running.
You mean there is no guarantee that even if SM is UP and we have some
hard coded entries of path record corresponding to some node X, we are
not sure that node X has actually come up or not?  In that case
actually that path resolving should fail if node has not come up, but
with the hard coding still path will be resolved?
>
> The main benefit I see to pre-loading the cache is to avoid SA storms
> when booting a large cluster.
that's true. Also cache will get valid entries only if network is
configured by SM otherwise every node SA will, possibly, drop SA
packets.
>
> - Sean
>