linux-kernel - Re: [PATCH v4 15/24] thermal: intel: hfi: Report the IPC class score of a CPU

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Message-ID: <CAJZ5v0igcMC=u0yQdAiB=tU6N68GCjVg4Y+7D6YA4XuZ4R0Z9w@mail.gmail.com>
Date:   Thu, 29 Jun 2023 20:56:36 +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>,
        Zhao Liu <zhao1.liu@...el.com>,
        "Yuan, Perry" <Perry.Yuan@....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>,
        Zhao Liu <zhao1.liu@...ux.intel.com>
Subject: Re: [PATCH v4 15/24] thermal: intel: hfi: Report the IPC class score
 of a CPU

On Tue, Jun 13, 2023 at 6:23 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.
>
> Use the cached per-CPU IPCC scores. A seqcount provides lockless access and
> the required memory ordering to avoid stale data.
>
> 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: Perry Yuan <Perry.Yuan@....com>
> 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: Zhao Liu <zhao1.liu@...ux.intel.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>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
> Changes since v3:
>  * Ordered memory loads using a seqcount.
>  * Removed local variable hfi_class from intel_hfi_get_ipcc_score().
>    (Rafael).
>
> 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   |  4 ++++
>  drivers/thermal/intel/intel_hfi.c | 40 +++++++++++++++++++++++++++++--
>  2 files changed, 42 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index 7d2ed7f7bb8c..8dd328cdb5cf 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -237,13 +237,17 @@ void init_freq_invariance_cppc(void);
>
>  #ifdef CONFIG_INTEL_HFI_THERMAL
>  int intel_hfi_read_classid(u8 *classid);
> +unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu);
>  #else
>  static inline int intel_hfi_read_classid(u8 *classid) { return -ENODEV; }
> +static inline unsigned long
> +intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu) { return -ENODEV; }
>  #endif
>
>  #ifdef CONFIG_IPC_CLASSES
>  void intel_update_ipcc(struct task_struct *curr);
>  #define arch_update_ipcc intel_update_ipcc
> +#define arch_get_ipcc_score intel_hfi_get_ipcc_score
>  #endif
>
>  #endif /* _ASM_X86_TOPOLOGY_H */
> diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> index d822ed0bb5c1..fec2c01fda1b 100644
> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -199,6 +199,42 @@ static int alloc_hfi_ipcc_scores(void)
>         return hfi_ipcc_scores ? 0 : -ENOMEM;
>  }
>
> +unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu)
> +{
> +       int *scores, score;
> +       unsigned long seq;
> +
> +       scores = per_cpu_ptr(hfi_ipcc_scores, cpu);
> +       if (!scores)
> +               return -ENODEV;
> +
> +       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().
> +        */
> +       if (ipcc >= hfi_features.nr_classes + 1)
> +               return -EINVAL;
> +
> +       /*
> +        * The seqcount implies load-acquire semantics to order loads with
> +        * lockless stores of the write side in set_hfi_ipcc_score(). It
> +        * also implies a compiler barrier.
> +        */
> +       do {
> +               seq = read_seqcount_begin(&hfi_ipcc_seqcount);
> +               /* @ipcc is never 0. */
> +               score = scores[ipcc - 1];
> +       } while (read_seqcount_retry(&hfi_ipcc_seqcount, seq));
> +
> +       return score;
> +}
> +
>  static void set_hfi_ipcc_scores(struct hfi_instance *hfi_instance)
>  {
>         int cpu;
> @@ -213,8 +249,8 @@ static void set_hfi_ipcc_scores(struct hfi_instance *hfi_instance)
>         raw_spin_lock_irq(&hfi_instance->table_lock);
>         /*
>          * The seqcount implies store-release semantics to order stores with
> -        * lockless loads from the seqcount read side. It also implies a
> -        * compiler barrier.
> +        * lockless loads from the seqcount read side in
> +        * intel_hfi_get_ipcc_score(). It also implies a compiler barrier.
>          */
>         write_seqcount_begin(&hfi_ipcc_seqcount);
>         for_each_cpu(cpu, hfi_instance->cpus) {
> --
> 2.25.1
>