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

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Date:   Mon, 27 Mar 2023 19:03:08 +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 21/24] thermal: intel: hfi: Implement model-specific
 checks for task classification

On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@...ux.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@...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 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.

> +
> +static bool classification_is_accurate(u8 hfi_class, bool smt_siblings_idle)
> +{
> +       switch (boot_cpu_data.x86_model) {
> +       case INTEL_FAM6_ALDERLAKE:
> +       case INTEL_FAM6_ALDERLAKE_L:
> +       case INTEL_FAM6_RAPTORLAKE:
> +       case INTEL_FAM6_RAPTORLAKE_P:
> +       case INTEL_FAM6_RAPTORLAKE_S:
> +               if (hfi_class == 3 || hfi_class == 2 || smt_siblings_idle)
> +                       return true;
> +
> +               return false;
> +
> +       default:
> +               return true;
> +       }
> +}
> +
>  void intel_hfi_update_ipcc(struct task_struct *curr)
>  {
>         union hfi_thread_feedback_char_msr msr;
> +       bool idle;
>
>         /* We should not be here if ITD is not supported. */
>         if (!cpu_feature_enabled(X86_FEATURE_ITD)) {
> @@ -227,7 +283,9 @@ void intel_hfi_update_ipcc(struct task_struct *curr)
>          * 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;
> +       idle = sched_smt_siblings_idle(task_cpu(curr));
> +       if (classification_is_accurate(msr.split.classid, idle))
> +               debounce_and_update_class(curr, msr.split.classid + 1);
>  }

I still think that this function should just return a number, possibly
including a special "no IPCC" value.  It may be passed a bool argument
indicating whether or not the SMT siblings are idle.

>
>  unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu)
> --