linux-kernel - Re: [PATCH] intel_idle: introduce 'use_acpi

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Message-ID: <afbe2137-398b-4053-93e7-2a03aeb32220@redhat.com>
Date: Tue, 4 Feb 2025 07:52:45 -0500
From: David Arcari <darcari@...hat.com>
To: dedekind1@...il.com, linux-pm@...r.kernel.org
Cc: Jonathan Corbet <corbet@....net>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>, Len Brown <lenb@...nel.org>,
 Prarit Bhargava <prarit@...hat.com>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] intel_idle: introduce 'use_acpi_cst' module parameter


Hi Artem,

On 2/4/25 7:23 AM, Artem Bityutskiy wrote:
> Hi David,
> 
> On Tue, 2025-01-28 at 09:11 -0500, David Arcari wrote:
> 
>> +The ``use_acpi_cst`` module parameter (recognized by ``intel_idle`` if the
>> +kernel has been configured with ACPI support) can be set to make the driver
>> +ignore the per cpu idle states in lieu of ACPI idle states. ``use_acpi_cst``
>> +has no effect if ``no_acpi`` is set).
> 
> With this change, there will be three parameters:
> 
> * no_acpi
> * use_acpi
> * use_acpi_cst
> 
> I would like to make the naming as intuitive as possible. We do not rename the
> first 2, but for the 3rd one, I think "force_acpi" would be a better name. Or
> perhaps "no_native"?

The problem with force_acpi is it is very similar to force_use_acpi 
which is what intel_idle.c uses internally:

drivers/idle/intel_idle.c:module_param_named(use_acpi, force_use_acpi, 
bool, 0444);

That said, I am not attached to the 'use_acpi_cst' parameter name.

> 
> * no_acpi - Do not use ACPI at all. Only native mode is available, no ACPI mode.
> * use_acpi - No-op in ACPI mode, consult ACPI tables for C-states on/off
>    status in native mode.
> * force_acpi (or no_native?) - Work only in ACPI mode, no native mode available
>    (ignore all custom tables).
> 
> Additionally, I think we should enhance the documentation for 'no_acpi' and
> 'use_acpi' while we're at it. Otherwise, it is hard to distinguish between these
> three options. Would you consider another patch that improves the documentation
> for 'no_acpi' and 'use_acpi', and then adds the third parameter?

I'm happy to resubmit. I guess I could use 'no_native' for the new 
parameter and then update the documentation as you suggest above.

Does that work?

> 
> Thanks, Artem!
> 

Best,
-DA