[ofa-general] OpenSM Up-Down algorithm

[Eitan Zahavi]

Hi Hal, Sagi,
> 
> On Sun, 2007-06-10 at 11:59, Sagi Schlanger wrote:
> > Hi,
> >  
> > I'm looking for some answers on Up-Down routing at OpenSM .
> >  
> > Is anybody familiar with a utility/procedure to find credit loops 
> > given a topology and routing settings?
> 
> I know there was at least talk of ibdiagnet (in ibutils) 
> checking this.
> Not sure if it is implemented (yet) or if it is routing 
> algorithm independent. Eitan ?
> 
> > Is there a handy spec describing the OpenSM Up-Down algorithm?
> 
> The OpenSM up/down routing is based on the following paper:
> 
> "Effective Strategy to Compute Forwarding Tables for 
> InfiniBand Networks"
> Jose Carlos Sancho, Universidad Politécnica de Valencia 
> Antonio Robles, Universidad Politécnica de Valencia Jose 
> Duato, Universidad Politécnica de Valencia
> 
> http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/
> dl/proceedings/&toc=comp/proceedings/icpp/2001/1257/00/1257toc
> .xml&DOI=10.1109/ICPP.2001.952046
> 
> > What is the scheme through which roots are defined on clos and non 
> > clos/fat tree topologies?
> 
> The admin can supply the roots via -a  <guid_list_file> 
> option when invoking OpenSM.
> 
>        Auto-detect root nodes - based on the CA hop length 
> from any switch
>        in  the  subnet,  a statistical histogram is built for 
> each switch (hop
>        num vs number of occurrences). If the  histogram  
> reflects  a  specific
>        column  (higher than others) for a certain node, then 
> it is marked as a
>        root node. Since the algorithm is statistical, it may 
> not find any root
>        nodes.  The  list  of the root nodes found by this 
> auto-detect stage is
>        used by the ranking process stage.
> 
>            Note 1: The user can override the node list manually.
>            Note 2: If this stage cannot find any root nodes, 
> and the user did
>                    not specify a guid list file, OpenSM 
> defaults back to the
>                    Min Hop routing algorithm.
> 
> > Is this algorithm always credit loop free?
> 
YES IT IS
> It's supposed to be.
> 
> > How efficient is using this algorithm on non clos/fat tree 
> topologies?
> 
> What do you mean by efficiency ? Also, are you asking about 
> pure fat tree or non pure fat tree (or both) ?
> 
> -- Hal
> 
> > Thanks for your cooperation,
> > Sagi
> > 
> > ____________________________________________________________
> > Sagi Schlanger  | +972-9-9717651 (o)   |   +972-52-2385154 (m)
> > Software Engineer, IB Switch
> > Voltaire - The Grid Backbone
> >  
> >  www.voltaire.com
> > 
> >  
> > 
> > 
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