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

[weiny2 at llnl.gov]

> 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

Ira