Re: [v1,net-next, 1/2] ethtool: add setting frame preemption of traffic classes

[Murali Karicheri]

Hi Vladimir,

On 01/23/2020 08:30 AM, Vladimir Oltean wrote:
> Hi Murali,
>
> On Wed, 22 Jan 2020 at 20:04, Murali Karicheri <m-karicheri2@xxxxxx> wrote:
> > I have question about the below parameters in The Gate Parameter Table
> > that are not currently supported by tc command. Looks like they need to
> > be shown to user for management.
> >
> >       - ConfigChange - Looks like this needs to be controlled by
> >         user. After sending admin command, user send this trigger to start
> >         copying admin schedule to operation schedule. Is this getting
> >         added to tc command?
>
> "The ConfigChange parameter signals the start of a
> configuration change for the gate
> when it is set to TRUE. This should only be done
> when the various administrative parameters
> are all set to appropriate values."
>
> As far as my understanding goes, all tc-taprio commands currently
> behave as though this boolean is implicitly set to TRUE after the
> structures have been set up. I'm not sure there is any value in doing
> otherwise.
That is my understanding as well. However I found this in the 802.1Q
and want to see if someone has insight into this parameter. So perhaps
we can ignore this for now and re-visit when there is a real need for
the same.

> >       - ConfigChangeTime - The time at which the administrative variables
> >         that determine the cycle are to be copied across to the
> >         corresponding operational variables, expressed as a PTP timescale
>
> This is the base-time of the admin schedule, no?

I think there is cycle time extension possible and in that case,
ConfigChangeTime may be different from Admin  base-time. So this gives
the actual time when the cycle configuration is actually applied.

> "The PTPtime at which the next config change is scheduled to occur.
> The value is a representation of a PTPtime value,
> consisting of a 48-bit integer
> number of seconds and a 32-bit integer number of nanoseconds."
>
> >       - TickGranularity - the management parameters specified in Gate
> >         Parameter Table allow a management station to discover the
> >         characteristics of an implementationâs cycle timer clock
> >         (TickGranularity) and to set the parameters for the gating cycle
> >         accordingly.
>
> Not sure who is going to use this and for what purpose, but ok.

Same here. Not sure how this will be used by application.

> >       - ConfigPending - A Boolean variable, set TRUE to indicate that
> >         there is a new cycle configuration awaiting installation.
>
> I had tried to export something like this (driver calls back into
> sch_taprio.c when hw has applied the config, this would result in
> ConfigPending = FALSE), but ultimately didn't finish the idea, and it
> caused some problems too, due to incorrect RCU usage.

Ok. Hope you plan to send a patch for this in the future.

> >       - ConfigChangeError - Error in configuration (AdminBaseTime <
> >         CurrentTime)
>
> This can be exported similarly.

Ok.

> >       - SupportedListMax - Maximum supported Admin/Open shed list.
> >
> > Is there a plan to export these from driver through tc show or such
> > command? The reason being, there would be applications developed to
> > manage configuration/schedule of TSN nodes that would requires these
> > information from the node. So would need a support either in tc or
> > some other means to retrieve them from hardware or driver. That is my
> > understanding...
>
> Not sure what answer you expect to receive for "is there any plan".

To avoid duplicating the work if someone is already working on this.

> You can go ahead and propose something, as long as it is reasonably
> useful to have.
Ok. Will keep in mind.
> > Regards,
> >
> > Murali
> >
> > --
> > Murali Karicheri
> > Texas Instruments
>
> Thanks,
> -Vladimir

--
Murali Karicheri
Texas Instruments