[openib-general] OSM: Using lid matrices in ucast manager

[Sasha Khapyorsky]

Hi Yevgeny,

On Tue, 2006-12-19 at 01:33 +0200, Yevgeny Kliteynik wrote:
> Hi Hal.
> 
>  
> 
> I have a question about some patch that I want to send regarding lid
> matrices usage in osm ucast
> 
> manager:
> 
>  
> 
> The FatTree routing doesn’t use the min hop tables, so we can skip the
> lid matrices building in OSM.

The lid matrices are used in mcast_mgr for multicast routes generation.

> However, ucast manager uses these lid matrices also to get the max lid
> that is accessible from each
> 
> switch, which defines the LTF table size.
> 
> This max lid is obtained by calling osm_switch_get_max_lid_ho()
> function, which in turn, calls 
> 
> osm_lid_matrix_get_max_lid_ho() for the switch’s lid matrix.
> 
> If the lid matrices weren’t built, then the
>  osm_switch_get_max_lid_ho() function will return 0xFFFF,
> 
> and eventually osm will crash.
> 
>  
> 
> Of course, I don’t want to build all the lid matrices just to know the
> max lid, so here’s what I’ve done:
> 
>  
> 
>       * I added a field to the osm_switch_t object: max_lid_ho (with
>         default value 0xFFFF, should it 
>         be 0x0 instead?).

Good thing. 0 is fine as default value IMHO.

>       * Added and three osm_switch_t methods for this new field:
>         getter, setter, and is_set that returns
>         true if this field has been set.

Why those methods? Everything you need is to access structure field and
'if (sw->max_lid_ho)' for "is_set" checks.

>       * The original osm_switch_get_max_lid_ho() has been updated to
>         return this field value if it’s set.
>       * Then in FatTree routing I set this field for each switch (I
>         get the max lid ‘for free’ as a byproduct
>         of the algorithm).
>       * Now everything in the ucast manager works fine, except for the
>         following two dump functions:
>                 __osm_ucast_mgr_dump_ucast_routes (it uses hops)
>                 ucast_mgr_dump_lid_matrix (obviously…)
>         These two functions check at the beginning whether the
>         max_lid_ho was set (using the ‘is_set’
>         method), and return w/o printing anything if the answer is
>         yes.
> 
>  
> 
> This way any other routing engine that uses lid matrix is not affected
> by this change, and any routing 
> 
> engine that doesn’t use the lid matrix has a way to set the max lid
> per switch explicitly.

Hope you are adding this for existing code.

> This approach works great, but I have a feeling that this is kinda
> hack…

Moving max_lid(_ho) to switch structure looks like a good idea for me
regardless to lid matrix build elimination.

The only problem I can see with lid matrices is mcast_mgr which uses
this.

Sasha

> 
>  
> 
> What do you think about this solution?
> 
> Any other suggestions?
> 
>  
> 
> Anyway, just wanted to hear your opinion before sending the patch.
> 
>    
> 
> Regards,
> 
>  
> 
> Yevgeny Kliteynik
> 
>  
> 
> Mellanox Technologies LTD
> 
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> 
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> 
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> 
>  
> 
>