Re: [PATCH v3 15/24] thermal: intel: hfi: Report the IPC class score of a CPU

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

On Mon, Mar 27, 2023 at 06:50:13PM +0200, Rafael J. Wysocki wrote:
> On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
> <ricardo.neri-calderon@linux.intel.com> wrote:
> >
> > Implement the arch_get_ipcc_score() interface of the scheduler. Use the
> > performance capabilities of the extended Hardware Feedback Interface table
> > as the IPC score.
> >
> > 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 returned HFI class (which starts at 0) to match the
> >    scheduler IPCC class (which starts at 1). (PeterZ)
> >  * Used the new interface names.
> > ---
> >  arch/x86/include/asm/topology.h   |  2 ++
> >  drivers/thermal/intel/intel_hfi.c | 27 +++++++++++++++++++++++++++
> >  2 files changed, 29 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> > index ffcdac3f398f..c4fcd9c3c634 100644
> > --- a/arch/x86/include/asm/topology.h
> > +++ b/arch/x86/include/asm/topology.h
> > @@ -229,8 +229,10 @@ void init_freq_invariance_cppc(void);
> >
> >  #if defined(CONFIG_IPC_CLASSES) && defined(CONFIG_INTEL_HFI_THERMAL)
> >  void intel_hfi_update_ipcc(struct task_struct *curr);
> > +unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu);
> >
> >  #define arch_update_ipcc intel_hfi_update_ipcc
> > +#define arch_get_ipcc_score intel_hfi_get_ipcc_score
> >  #endif /* defined(CONFIG_IPC_CLASSES) && defined(CONFIG_INTEL_HFI_THERMAL) */
> >
> >  #endif /* _ASM_X86_TOPOLOGY_H */
> > diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> > index 530dcf57e06e..fa9b4a678d92 100644
> > --- a/drivers/thermal/intel/intel_hfi.c
> > +++ b/drivers/thermal/intel/intel_hfi.c
> > @@ -206,6 +206,33 @@ void intel_hfi_update_ipcc(struct task_struct *curr)
> >         curr->ipcc = msr.split.classid + 1;
> >  }
> >
> > +unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu)
> > +{
> > +       unsigned short hfi_class;
> 
> It looks like the variable above is only used to save a subtraction or
> addition of 1 to something going forward.
> 
> > +       int *scores;
> > +
> > +       if (cpu < 0 || cpu >= nr_cpu_ids)
> > +               return -EINVAL;
> > +
> > +       if (ipcc == IPC_CLASS_UNCLASSIFIED)
> > +               return -EINVAL;
> > +
> > +       /*
> > +        * Scheduler IPC classes start at 1. HFI classes start at 0.
> > +        * See note intel_hfi_update_ipcc().
> > +        */
> > +       hfi_class = ipcc - 1;
> > +
> > +       if (hfi_class >= hfi_features.nr_classes)
> 
> Personally, I would do
> 
> if (ipcc >= hfi_features.nr_classes + 1)
> 
> here and ->
> 
> > +               return -EINVAL;
> > +
> > +       scores = per_cpu_ptr(hfi_ipcc_scores, cpu);
> > +       if (!scores)
> > +               return -ENODEV;
> > +
> 
> -> scores[ipcc - 1]

Sure, I can get rid of hfi_class.

> 
> below.
> 
> > +       return READ_ONCE(scores[hfi_class]);
> 
> And why does this need to use READ_ONCE()?

This is the corresponding read of the WRITE_ONCE in patch 13. The CPU
handling the HFI interrupt, very likely a different CPU, updates
scores[hfi_class]. My intention is to let that write to complete before
reading the score here.
> 
> > +}
> > +
> >  static int alloc_hfi_ipcc_scores(void)
> >  {
> >         if (!cpu_feature_enabled(X86_FEATURE_ITD))
> > --