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

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Date:   Mon, 27 Mar 2023 18:50:13 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Lukasz Luba <lukasz.luba@....com>,
        Ionela Voinescu <ionela.voinescu@....com>, x86@...nel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v3 15/24] thermal: intel: hfi: Report the IPC class score
 of a CPU

On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@...ux.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@...gle.com>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Ionela Voinescu <ionela.voinescu@....com>
> Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Lukasz Luba <lukasz.luba@....com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Tim C. Chen <tim.c.chen@...el.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: x86@...nel.org
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.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]

below.

> +       return READ_ONCE(scores[hfi_class]);

And why does this need to use READ_ONCE()?

> +}
> +
>  static int alloc_hfi_ipcc_scores(void)
>  {
>         if (!cpu_feature_enabled(X86_FEATURE_ITD))
> --