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

[Hal Rosenstock]

On Thu, 2007-05-17 at 01:21, Devesh Sharma wrote:
> 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,

How does the admin know they are valid ? Are they somehow preconfigured
at the SM ? Doesn't each SM have its own policy for generating valid PRs
? Or are these from a live SM and just loaded "out of band" to
bypass/preclude the SA PR mechanism ?

-- Hal

>  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
> >
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