linux-kernel - Re: [PATCH v4] intel_idle: introduce 'no

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Message-ID: <CAJZ5v0gUfp+ueLMr1arwgK0r3WAQmfbb7YB54oZP-ySkD0q6YQ@mail.gmail.com>
Date: Wed, 19 Feb 2025 22:27:46 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: David Arcari <darcari@...hat.com>
Cc: linux-pm@...r.kernel.org, Jonathan Corbet <corbet@....net>, Len Brown <lenb@...nel.org>, 
	Artem Bityutskiy <dedekind1@...il.com>, Prarit Bhargava <prarit@...hat.com>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] intel_idle: introduce 'no_native' module parameter

On Thu, Feb 13, 2025 at 5:07 PM David Arcari <darcari@...hat.com> wrote:
>
> Since commit 18734958e9bf ("intel_idle: Use ACPI _CST for processor models
> without C-state tables") the intel_idle driver has had the ability to use
> the ACPI _CST to populate C-states when the processor model is not
> recognized. However, even when the processor model is recognized (native
> mode) there are cases where it is useful to make the driver ignore the per
> cpu idle states in lieu of ACPI C-states (such as specific application
> performance). Add the 'no_native' module parameter to provide this
> functionality.
>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Len Brown <lenb@...nel.org>
> Cc: David Arcari <darcari@...hat.com>
> Cc: Artem Bityutskiy <dedekind1@...il.com>
> Cc: Prarit Bhargava <prarit@...hat.com>
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: David Arcari <darcari@...hat.com>
> ---
> v4: fix !CONFIG_ACPI_PROCESSOR_CSTATE compilation issue
> v3: more documentation cleanup
> v2: renamed parameter, cleaned up documentation
>
> Documentation/admin-guide/pm/intel_idle.rst | 18 +++++++++++++-----
>  drivers/idle/intel_idle.c                   | 16 ++++++++++++++++
>  2 files changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst
> index 39bd6ecce7de..5940528146eb 100644
> --- a/Documentation/admin-guide/pm/intel_idle.rst
> +++ b/Documentation/admin-guide/pm/intel_idle.rst
> @@ -192,11 +192,19 @@ even if they have been enumerated (see :ref:`cpu-pm-qos` in
>  Documentation/admin-guide/pm/cpuidle.rst).
>  Setting ``max_cstate`` to 0 causes the ``intel_idle`` initialization to fail.
>
> -The ``no_acpi`` and ``use_acpi`` module parameters (recognized by ``intel_idle``
> -if the kernel has been configured with ACPI support) can be set to make the
> -driver ignore the system's ACPI tables entirely or use them for all of the
> -recognized processor models, respectively (they both are unset by default and
> -``use_acpi`` has no effect if ``no_acpi`` is set).
> +The ``no_acpi``, ``use_acpi`` and ``no_native`` module parameters are
> +recognized by ``intel_idle`` if the kernel has been configured with ACPI
> +support.  In the case that ACPI is not configured these flags have no impact
> +on functionality.
> +
> +``no_acpi`` - Do not use ACPI at all.  Only native mode is available, no
> +ACPI mode.
> +
> +``use_acpi`` - No-op in ACPI mode, the driver will consult ACPI tables for
> +C-states on/off status in native mode.
> +
> +``no_native`` - Work only in ACPI mode, no native mode available (ignore
> +all custom tables).
>
>  The value of the ``states_off`` module parameter (0 by default) represents a
>  list of idle states to be disabled by default in the form of a bitmask.
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index 118fe1d37c22..b0be5ef43ffc 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -1695,6 +1695,10 @@ static bool force_use_acpi __read_mostly; /* No effect if no_acpi is set. */
>  module_param_named(use_acpi, force_use_acpi, bool, 0444);
>  MODULE_PARM_DESC(use_acpi, "Use ACPI _CST for building the idle states list");
>
> +static bool no_native __read_mostly; /* No effect if no_acpi is set. */
> +module_param_named(no_native, no_native, bool, 0444);
> +MODULE_PARM_DESC(no_native, "Ignore cpu specific (native) idle states in lieu of ACPI idle states");
> +
>  static struct acpi_processor_power acpi_state_table __initdata;
>
>  /**
> @@ -1834,6 +1838,11 @@ static bool __init intel_idle_off_by_default(unsigned int flags, u32 mwait_hint)
>         }
>         return true;
>  }
> +
> +static inline bool ignore_native(void)
> +{
> +       return no_native & !no_acpi;
> +}
>  #else /* !CONFIG_ACPI_PROCESSOR_CSTATE */
>  #define force_use_acpi (false)
>
> @@ -1843,6 +1852,7 @@ static inline bool intel_idle_off_by_default(unsigned int flags, u32 mwait_hint)
>  {
>         return false;
>  }
> +static inline bool ignore_native(void) { return false; }
>  #endif /* !CONFIG_ACPI_PROCESSOR_CSTATE */
>
>  /**
> @@ -2328,6 +2338,12 @@ static int __init intel_idle_init(void)
>         pr_debug("MWAIT substates: 0x%x\n", mwait_substates);
>
>         icpu = (const struct idle_cpu *)id->driver_data;
> +       if (ignore_native()) {
> +               if (icpu) {
> +                       pr_debug("ignoring native cpu idle states\n");
> +                       icpu = NULL;
> +               }
> +       }

Why not

+       if (icpu && ignore_native()) {
+              pr_debug("disregarding built-in CPU idle states table\n");
+              icpu = NULL;
+       }

>         if (icpu) {
>                 if (icpu->state_table)
>                         cpuidle_state_table = icpu->state_table;
> --