Re: Default force_link_speed value in opensm configuration

[Ira Weiny <weiny2-i2BcT+NCU+M@public.gmane.org>]

On Tue, 13 Oct 2009 09:39:08 -0400
Hal Rosenstock <hal.rosenstock-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> On Mon, Oct 12, 2009 at 5:35 PM, Ira Weiny <weiny2-i2BcT+NCU+M@public.gmane.org> wrote:
> > On Mon, 12 Oct 2009 11:47:37 +0200
> > "Eli Dorfman (Voltaire)" <dorfman.eli-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> >> Ira Weiny wrote:
> >> > On Tue, 06 Oct 2009 17:56:01 +0200
> >> > "Eli Dorfman (Voltaire)" <dorfman.eli-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> >
> >> >> Hi,
> >> >>
> >> >> Is there a reason for setting default force_link_speed to 15 (set enabled as supported)
> >> >> and not to 0 (don't modify PortInfo:LinkSpeedEnabled )?
> 
> This is going back some 2 years to 7/15/07 commit ID
> c7cbf11992b111d2b9c7347e398e67f2b5806edb
> 
> commit c7cbf11992b111d2b9c7347e398e67f2b5806edb
> Author: Hal Rosenstock <halr-smomgflXvOZWk0Htik3J/w@public.gmane.org>
> Date:   Sun Jul 15 06:43:20 2007 -0400
> 
>     OpenSM: Change force_link_speed to allow for local policy and more flexibili
> 
>     OpenSM: Change force_link_speed to allow for local policy and more
>     flexibility
> 
>     Extend (and change) the use of force_link_speed as follows:
>     0 - no change
>     1 - set to SDR
>     15 - set as supported (default)
>     (Non zero values are used to set LinkSpeedEnabled component in PortInfo)
> 
>     Note that force_link_speed 0 which used to force SDR is now
>     force_link_speed 1
> 
>     "Ideally", there were be a per port configuration of this.

BTW I have a patch which allows a user to except some nodes from this
restriction.  I don't know that anyone but us is using this "feature" so I did
not submit the patch.  If someone else would like some finer granularity I can
clean up the patch and make it available.

> 
>     [Note this is largely untested.]

BTW, now, this is highly tested, to force SDR, on some of our clusters!
Thanks!

> 
>     Signed-off-by: Hal Rosenstock <hal.rosenstock-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 
> I think that the default was chosen based on IBA 1.2.1 vol 2 p. 108 stating:
> "The default value following power on shall be set to LinkSpeedSupported."
> which should not be an issue with compliant hardware.
> 

[snip]

> >
> > However, I would like to know if anyone else knows of hardware which needs it
> > set to "15".  If so, this is going to be an interesting problem...  ;-)
> 
> I'm not sure about need but I think there is a tradeoff here in
> changing this. The pro is it will work with non compliant hardware.
> The con is that it may result in less than the max LSS being used in
> some scenarios.
> 
> Should the default be changed for non compliant hardware or should
> this need to be configured in subnets including such hardware as it
> has since this was introduced ?
> 

I think that is a good way of thinking about things.

Ira

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