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

[Devesh Sharma]

On 17 May 2007 06:42:16 -0400, Hal Rosenstock <halr at voltaire.com> wrote:
> 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 ?
Depending on the initial application runs, some trusted PRs can be generated.
>Are they somehow preconfigured at the SM ?
I am not sure about SM has any such provision? Also not sure about the
role of SM in path resolving. I mean once node has initiated SA query,
whether SM has some database to reply SA or On the fly destination
node is contacted to get asked path recored?
>Doesn't each SM have its own policy for generating valid PRs ?
Ultimately path record is in Path_Record object format, and SA cache
is going to store in a fixed manner, How generation policy matters?
CMIIW. Also I am assuming a homogeneous cluster where certain
parameters can be assumed to be same always.
>are these from a live SM and just loaded "out of band" to
bypass/preclude the SA PR >mechanism ?
may be
>
> -- 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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