linux-kernel - Re: [PATCH v3 16/24] thermal: intel: hfi: Define a default class for unclassified tasks

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Date:   Mon, 27 Mar 2023 18:51:33 +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 16/24] thermal: intel: hfi: Define a default class for
 unclassified tasks

On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@...ux.intel.com> wrote:
>
> A task may be unclassified if it has been recently created, spend most of
> its lifetime sleeping, or hardware has not provided a classification.
>
> Most tasks will be eventually classified as scheduler's IPC class 1
> (HFI class 0). This class corresponds to the capabilities in the legacy,
> classless, HFI table.
>
> IPC class 1 is a reasonable choice until hardware provides an actual
> classification. Meanwhile, the scheduler will place classes of tasks with
> higher IPC scores on higher-performance CPUs.
>
> 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>

Fine with me, so

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

> ---
> Changes since v2:
>  * None
>
> Changes since v1:
>  * Now the default class is 1.
> ---
>  drivers/thermal/intel/intel_hfi.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> index fa9b4a678d92..7ea6acce7107 100644
> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -185,6 +185,19 @@ static struct workqueue_struct *hfi_updates_wq;
>  #ifdef CONFIG_IPC_CLASSES
>  static int __percpu *hfi_ipcc_scores;
>
> +/*
> + * A task may be unclassified if it has been recently created, spend most of
> + * its lifetime sleeping, or hardware has not provided a classification.
> + *
> + * Most tasks will be classified as scheduler's IPC class 1 (HFI class 0)
> + * eventually. Meanwhile, the scheduler will place classes of tasks with higher
> + * IPC scores on higher-performance CPUs.
> + *
> + * IPC class 1 is a reasonable choice. It matches the performance capability
> + * of the legacy, classless, HFI table.
> + */
> +#define HFI_UNCLASSIFIED_DEFAULT 1
> +
>  void intel_hfi_update_ipcc(struct task_struct *curr)
>  {
>         union hfi_thread_feedback_char_msr msr;
> @@ -215,7 +228,7 @@ unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu)
>                 return -EINVAL;
>
>         if (ipcc == IPC_CLASS_UNCLASSIFIED)
> -               return -EINVAL;
> +               ipcc = HFI_UNCLASSIFIED_DEFAULT;
>
>         /*
>          * Scheduler IPC classes start at 1. HFI classes start at 0.
> --
> 2.25.1
>