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

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Message-ID: <ZnHSKiaYf2tIQo58@kf-XE>
Date: Tue, 18 Jun 2024 13:30:02 -0500
From: Aaron Rainbolt <arainbolt@...cus.org>
To: mario.limonciello@....com
Cc: linux-acpi@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
	linux-kernel@...r.kernel.org, mmikowski@...cus.org,
	Perry.Yuan@....com
Subject: Re: [PATCH] acpi: Allow ignoring _OSC CPPC v2 bit via kernel
 parameter

On Tue, Jun 18, 2024 at 12:09:19PM -0500, Mario Limonciello wrote:
> On 6/17/2024 21:54, 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.
> > 
> > To work around this, provide a new kernel parameter,
> > "processor.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.
> > 
> > Tested-by: Michael Mikowski <mmikowski@...cus.org>
> > Signed-off-by: Aaron Rainbolt <arainbolt@...cus.org>
> 
> This sounds like a platform bug and if we do accept a patch like this I
> think we need a lot more documentation about the situation.

It is a platform bug, yes. See my previous email,                      
https://lore.kernel.org/linux-acpi/d01b0a1f-bd33-47fe-ab41-43843d8a374f@kfocus.org/T/#u
(I meant to send this email as a reply to that one, but failed to do so.)

> Can you please share more information about your hardware:
> 1) Manufacturer?

Carbon Systems, models Iridium 14 and Iridium 16.

> 2) CPU?

Intel Core i5-13500H.

> 3) Manufacturer firmware version?

The systems use an AMI BIOS with version N.1.10CAR01 according to
dmidecode. This is the latest BIOS available from the manufacturer.

> 4) If it's AMD what's the AGESA version?

Both affected systems are Intel-based and use heterogenous cores, not AMD.

> And most importantly do you have the latest system firmware version from
> your manufacturer?  If not; please upgrade that first.

We are using the latest firmware. (We're trying to work with the ODM to
potentially get a firmware update, but since this affects more than just
us and a firmware update may not be possible for everyone, this would
likely be worth providing a kernel-level workaround for.)

I can easily provide more detailed information - would the full output of
'dmidecode' and 'acpidump' be useful?