[ofa-general] opensm --lcm

[Sasha Khapyorsky]

Hi,

On 19:13 Mon 12 Nov     , Bernd Schubert wrote:
> 
> so far we always did run opensm without the --lmc option, but just recently I 
> read in opensm's manpage about it.
> 
> <opensm manpage>
> This option specifies the subnet's LMC value.  The number of LIDs assigned to 
> each port  is  2^LMC.   
> The LMC  value  must be in the range 0-7.  LMC values > 0 allow multiple paths 
> between ports.  LMC values > 0 should only be used if the subnet topology 
> actually provides multiple paths between ports, i.e.  multiple
> interconnects  between  switches.   Without -l, OpenSM defaults to LMC = 0, 
> which allows one path between any two ports.
> </opensm manpage>
> 
> In one of our configurations we do have a mts2400 (master) switch and 
> connected to it are two mts14400 switches (each with 3 connections to the the 
> mts2400).
> I think from the description of the opensm manpage we need to give the "--lmc" 
> to make use of the 3 connections from each mts14400 switch to the mts2400 
> switch, don't we?

In theory (AFAIR by default OpenSM will not assign LMC for Switch port 0
due to some chip bug), when target is switch itself. But if you have
end nodes connected to this switch and targets are end nodes when OpenSM
will try to use all links for it.

> Furthermore, from manpage I would think we even need this 
> option for proper inter-communication between the switch modules?

For switch modules yes, but again OpenSM will not assign LMC for
switches (even then --lmc specified), only for end nodes. In order to
enable it you will need to turn on 'lmc_esp0' option in OpenSM options
file. But as far as I remember it is not supported by switches now.

Sasha