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

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Message-ID: <Ymj3l6cdxfmQ+hb0@kroah.com>
Date:   Wed, 27 Apr 2022 09:58:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, sudeep.holla@....com,
        dietmar.eggemann@....com, vincent.guittot@...aro.org,
        rafael@...nel.org, rostedt@...dmis.org, mingo@...hat.com
Subject: Re: [PATCH v3] arch_topology: Trace the update thermal pressure

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@...el.com>
> > 
> > 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@intel.com/
> 
> 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.

thanks,

greg k-h