linux-kernel - Re: [PATCH v5] x86: intel_epb: Add earlyparam option to keep bias at performance

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Message-ID: <ff3a0382-734d-4f46-bd35-ffa1f53a3ac3@intel.com>
Date: Wed, 3 Jan 2024 07:17:46 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Jack Allister <jalliste@...zon.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
 Paul Durrant <pdurrant@...zon.com>, Jue Wang <juew@...zon.com>,
 Usama Arif <usama.arif@...edance.com>, Jonathan Corbet <corbet@....net>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 "Paul E. McKenney" <paulmck@...nel.org>, Randy Dunlap
 <rdunlap@...radead.org>, Tejun Heo <tj@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Yan-Jie Wang <yanjiewtw@...il.com>,
 Hans de Goede <hdegoede@...hat.com>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86: intel_epb: Add earlyparam option to keep bias at
 performance

On 1/3/24 06:46, Jack Allister wrote:
> +	intel_epb=	[X86]
> +			auto
> +			  Same as not passing a parameter to intel_epb. This will
> +			  ensure that the intel_epb module will restore the energy
> +			  performance bias to "normal" at boot-time. This workaround
> +			  is for buggy BIOSes which may not set this value and cause
> +			  either overheating or excess power usage.
> +			preserve
> +			  At kernel boot-time if the EPB value is read as "performance"
> +			  keep it at this value. This prevents the "performance" -> "normal"
> +			  transition which is a workaround mentioned above.

This ends up describing the nitty-gritty details of the implementation
instead of what users should take away from the options.  Could we up
level this a bit?

How about this?

	intel_epb=	[X86]

			auto (default)
				Work around buggy BIOSes to avoid
				excess power usage by forcing
				performance bias to "normal" at boot-
				time.

			preserve
				Do not override the existing performance
				bias setting.  Useful if a previous
				kernel or bootloader's setting is more
				desirable than "normal".

It's better formatted and uses the "(default)" tag instead of trying to
explain it in prose.  It also explains when someone might want to use
the override instead of just explaining its function.