linux-kernel - Re: [PATCH v3 14/24] thermal: intel: hfi: Update the IPC class of the current task

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Date:   Mon, 27 Mar 2023 18:42:28 +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 14/24] thermal: intel: hfi: Update the IPC class of the
 current task

On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@...ux.intel.com> wrote:
>
> Use Intel Thread Director classification to update the IPC class of a
> task. Implement the arch_update_ipcc() interface of the scheduler.
>
> 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:
>  * Removed the implementation of arch_has_ipc_classes().
>
> 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.
>  * Redefined union hfi_thread_feedback_char_msr to ensure all
>    bit-fields are packed. (PeterZ)
>  * Removed CONFIG_INTEL_THREAD_DIRECTOR. (PeterZ)
>  * Shortened the names of the functions that implement IPC classes.
>  * Removed argument smt_siblings_idle from intel_hfi_update_ipcc().
>    (PeterZ)
> ---
>  arch/x86/include/asm/topology.h   |  6 ++++++
>  drivers/thermal/intel/intel_hfi.c | 32 +++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
>
> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index 458c891a8273..ffcdac3f398f 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -227,4 +227,10 @@ void init_freq_invariance_cppc(void);
>  #define arch_init_invariance_cppc init_freq_invariance_cppc
>  #endif
>
> +#if defined(CONFIG_IPC_CLASSES) && defined(CONFIG_INTEL_HFI_THERMAL)
> +void intel_hfi_update_ipcc(struct task_struct *curr);
> +
> +#define arch_update_ipcc intel_hfi_update_ipcc
> +#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 b06021828892..530dcf57e06e 100644
> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -72,6 +72,17 @@ union cpuid6_edx {
>         u32 full;
>  };
>
> +#ifdef CONFIG_IPC_CLASSES
> +union hfi_thread_feedback_char_msr {
> +       struct {
> +               u64     classid : 8;
> +               u64     __reserved : 55;
> +               u64     valid : 1;
> +       } split;
> +       u64 full;
> +};
> +#endif
> +
>  /**
>   * struct hfi_cpu_data - HFI capabilities per CPU
>   * @perf_cap:          Performance capability
> @@ -174,6 +185,27 @@ static struct workqueue_struct *hfi_updates_wq;
>  #ifdef CONFIG_IPC_CLASSES
>  static int __percpu *hfi_ipcc_scores;
>
> +void intel_hfi_update_ipcc(struct task_struct *curr)
> +{
> +       union hfi_thread_feedback_char_msr msr;
> +
> +       /* We should not be here if ITD is not supported. */
> +       if (!cpu_feature_enabled(X86_FEATURE_ITD)) {
> +               pr_warn_once("task classification requested but not supported!");
> +               return;
> +       }
> +
> +       rdmsrl(MSR_IA32_HW_FEEDBACK_CHAR, msr.full);
> +       if (!msr.split.valid)
> +               return;
> +
> +       /*
> +        * 0 is a valid classification for Intel Thread Director. A scheduler
> +        * IPCC class of 0 means that the task is unclassified. Adjust.
> +        */
> +       curr->ipcc = msr.split.classid + 1;
> +}

Wouldn't it be better to return the adjusted value from this function
and let the caller store it where appropriate?

It doesn't look like it is necessary to pass the task_struct pointer to it.

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