Re: [PATCH v3] arch_topology: Trace the update thermal pressure

[Lukasz Luba]

On 4/27/22 08:58, Greg KH wrote:
> On Wed, Apr 27, 2022 at 08:52:50AM +0100, Lukasz Luba wrote:
> > On 4/27/22 08:44, Greg KH wrote:
> > > On Wed, Apr 27, 2022 at 08:35:51AM +0100, Lukasz Luba wrote:
> > > > Add trace event to capture the moment of the call for updating the thermal
> > > > pressure value. It's helpful to investigate how often those events occur
> > > > in a system dealing with throttling. This trace event is needed since the
> > > > old 'cdev_update' might not be used by some drivers.
> > > >
> > > > The old 'cdev_update' trace event only provides a cooling state
> > > > value: [0, n]. That state value then needs additional tools to translate
> > > > it: state -> freq -> capacity -> thermal pressure. This new trace event
> > > > just stores proper thermal pressure value in the trace buffer, no need
> > > > for additional logic. This is helpful for cooperation when someone can
> > > > simply sends to the list the trace buffer output from the platform (no
> > > > need from additional information from other subsystems).
> > > >
> > > > There are also platforms which due to some design reasons don't use
> > > > cooling devices and thus don't trigger old 'cdev_update' trace event.
> > > > They are also important and measuring latency for the thermal signal
> > > > raising/decaying characteristics is in scope. This new trace event
> > > > would cover them as well.
> > > >
> > > > We already have a trace point 'pelt_thermal_tp' which after a change to
> > > > trace event can be paired with this new 'thermal_pressure_update' and
> > > > derive more insight what is going on in the system under thermal pressure
> > > > (and why).
> > > >
> > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > >
> > > The kernel test robot did not report that you needed to add a new trace
> > > event :(
> >
> > I got feedback from the test robot for v1, which figured out that
> > the riscv configuration is broken. You can find it here
> > https://lore.kernel.org/lkml/202204201654.vcszVDGb-lkp@xxxxxxxxx/
> >
> > So, I've added that tag following:
> > "If you fix the issue, kindly add following tag as appropriate"
> >
> > Should this only be honored when a patch actually got into next
> > and then following patch with a fix would have that tag?
>
> Yes.  And you can mention it in the version information about what
> changed between each patch version below the --- line, but as is, you
> can see how this does not make sense.

Thank you Greg for the explanation. I'll remove the tag in v4.

Regards,
Lukasz