linux-kernel - Re: [PATCH V2 RFC] acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter

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Date: Tue, 18 Jun 2024 15:58:44 -0500
From: Aaron Rainbolt <arainbolt@...cus.org>
To: mario.limonciello@....com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: rafael@...nel.org, lenb@...nel.org, mmikowski@...cus.org,
	Perry.Yuan@....com
Subject: Re: [PATCH V2 RFC] acpi: Allow ignoring _OSC CPPC v2 bit via kernel
 parameter

On Tue, Jun 18, 2024 at 03:25:36PM -0500, Aaron Rainbolt wrote:
> acpi: Allow ignoring _OSC CPPC v2 bit via kernel parameter
> 
> The _OSC is supposed to contain a bit indicating whether the hardware
> supports CPPC v2 or not. This bit is not always set, causing CPPC v2 to
> be considered absent. This results in severe single-core performance
> issues with the EEVDF scheduler on heterogenous-core Intel processors.
> 
> To work around this, provide a new kernel parameter, "ignore_osc_cppc_bit",
> which may be used to ignore the _OSC CPPC v2 bit and act as if the bit was
> enabled. This allows CPPC to be properly detected even if not "enabled" by
> _OSC, allowing users with problematic hardware to obtain decent single-core
> performance.
> 
> Signed-off-by: Aaron Rainbolt <arainbolt@...cus.org>
> 
> ---
> 
> V1 -> V2: Rewrite to work in cpc_supported_by_cpu.
> 
> RFC: I have not yet tested this patch to ensure it functions properly,
>  nor have I attempted to compile it against mainline. My system takes
>  a couple of hours or so to build a kernel, and I'd like to submit this
>  for feedback now and test once it's sent.

I sped up my build by using a defconfig rather than a default menuconfig
(still learning how these things work), and confirmed that the patch does
build against 6.10~rc4. Will report back test results hopefully soon.