Re: [PATCH v3 21/24] thermal: intel: hfi: Implement model-specific checks for task classification

[Ricardo Neri <ricardo.neri-calderon@linux.intel.com>]

On Mon, Mar 27, 2023 at 07:03:08PM +0200, Rafael J. Wysocki wrote:
> On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
> <ricardo.neri-calderon@linux.intel.com> wrote:
> >
> > In Alder Lake and Raptor Lake, the result of thread classification is more
> > accurate when only one SMT sibling is busy. Classification results for
> > class 2 and 3 are always reliable.
> >
> > To avoid unnecessary migrations, only update the class of a task if it has
> > been the same during 4 consecutive user ticks.
> >
> > Cc: Ben Segall <bsegall@google.com>
> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > Cc: Ionela Voinescu <ionela.voinescu@arm.com>
> > Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
> > Cc: Len Brown <len.brown@intel.com>
> > Cc: Lukasz Luba <lukasz.luba@arm.com>
> > Cc: Mel Gorman <mgorman@suse.de>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Tim C. Chen <tim.c.chen@intel.com>
> > Cc: Valentin Schneider <vschneid@redhat.com>
> > Cc: x86@kernel.org
> > Cc: linux-pm@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > ---
> > Changes since v2:
> >  * None
> >
> > Changes since v1:
> >  * Adjusted the result the classification of Intel Thread Director to start
> >    at class 1. Class 0 for the scheduler means that the task is
> >    unclassified.
> >  * Used the new names of the IPC classes members in task_struct.
> >  * Reworked helper functions to use sched_smt_siblings_idle() to query
> >    the idle state of the SMT siblings of a CPU.
> > ---
> >  drivers/thermal/intel/intel_hfi.c | 60 ++++++++++++++++++++++++++++++-
> >  1 file changed, 59 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> > index 35d947f47550..fdb53e4cabc1 100644
> > --- a/drivers/thermal/intel/intel_hfi.c
> > +++ b/drivers/thermal/intel/intel_hfi.c
> > @@ -40,6 +40,7 @@
> >  #include <linux/workqueue.h>
> >
> >  #include <asm/msr.h>
> > +#include <asm/intel-family.h>
> >
> >  #include "../thermal_core.h"
> >  #include "intel_hfi.h"
> > @@ -209,9 +210,64 @@ static int __percpu *hfi_ipcc_scores;
> >   */
> >  #define HFI_UNCLASSIFIED_DEFAULT 1
> >
> > +#define CLASS_DEBOUNCER_SKIPS 4
> > +
> > +/**
> > + * debounce_and_update_class() - Process and update a task's classification
> > + *
> > + * @p:         The task of which the classification will be updated
> > + * @new_ipcc:  The new IPC classification
> > + *
> > + * Update the classification of @p with the new value that hardware provides.
> > + * Only update the classification of @p if it has been the same during
> > + * CLASS_DEBOUNCER_SKIPS consecutive ticks.
> > + */
> > +static void debounce_and_update_class(struct task_struct *p, u8 new_ipcc)
> > +{
> > +       u16 debounce_skip;
> > +
> > +       /* The class of @p changed. Only restart the debounce counter. */
> > +       if (p->ipcc_tmp != new_ipcc) {
> > +               p->ipcc_cntr = 1;
> > +               goto out;
> > +       }
> > +
> > +       /*
> > +        * The class of @p did not change. Update it if it has been the same
> > +        * for CLASS_DEBOUNCER_SKIPS user ticks.
> > +        */
> > +       debounce_skip = p->ipcc_cntr + 1;
> > +       if (debounce_skip < CLASS_DEBOUNCER_SKIPS)
> > +               p->ipcc_cntr++;
> > +       else
> > +               p->ipcc = new_ipcc;
> > +
> > +out:
> > +       p->ipcc_tmp = new_ipcc;
> > +}
> 
> Why does the code above belong to the Intel HFI driver?  It doesn't
> look like there is anything driver-specific in it.

That is a good point. This post-processing is specific to the
implementation of IPCC classes using Intel Thread Director.

Maybe a new file called drivers/thermal/intel/intel_itd.c would be better?