[ofa-general] Re: [PATCH] opensm/opensm/osm_subnet.c: add checks for HOQ and Leaf HOQ input values

[Hal Rosenstock]

On Wed, 2008-04-09 at 09:36 -0700, weiny2 at llnl.gov wrote:
> > On Wed, 2008-04-09 at 08:38 -0700, weiny2 at llnl.gov wrote:
> >> > On Wed, 2008-04-09 at 10:01 +0000, Sasha Khapyorsky wrote:
> >> >> Hi Ira,
> >> >>
> >> >> On 16:48 Tue 08 Apr     , weiny2 at llnl.gov wrote:
> >> >> > As per Hal's comments change the alternate value for [leaf] HOQ to
> >> be
> >> >> > "infinity" when the user specifies a value larger than "infinity".
> >> >>
> >> >> Actually I would prefer original version of the patch. The main
> >> reason
> >> >> is that infinite packet life time is really dangerous thing - in case
> >> >> when a fabric is routed with credit loops (very common case with
> >> default
> >> >> min-hops routing) it leads to total fabric stuck and not just to some
> >> >> performance degradation.
> >> >>
> >> >> So I think it is safer to reject invalid value and to set the default
> >> >> (log an error, etc.i). As it was done in the original version of the
> >> >> patch.
> >> >>
> >> >> Hal, do you agree?
> >> >
> >> > Safer yes but I think it is less to the intent of the admin who just
> >> > doesn't understand the max value for this and that's why I proposed
> >> this
> >> > change. My preference is to max it out but it comes down to a judgment
> >> > call. There's a downside either way.
> >>
> >> What if we set it to 0x13?  This would be the maximum value that will
> >> not
> >> "lock" up the fabric.  We could also add to the error message that the
> >> admin needs to specify 0x14 if they specifically want "infinity" to be
> >> set?
> >
> > So disallow the setting to infinity ?
> >
> 
> No, if you want infinity you have to specify 0x14 (19) in the opensm.opts
> file.  For example, specifying 100 will set the value to 0x13 and warn the
> user that if they want infinity they will have to specify it explicitly;
> ie head_of_queue_lifetime = 0x14

That's another choice but seems a little weird to me that 20 is infinite
and >20 is set less than that but this is a judgment call. Not sure what
others think. At this point, I have nothing more to add on this.

-- Hal

> Ira
> 
> 
>