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

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Message-ID: <a7790c74-2bec-4a24-b6e5-223c4e1ed372@amd.com>
Date: Tue, 18 Jun 2024 13:35:57 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Aaron Rainbolt <arainbolt@...cus.org>
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 6/18/2024 13:30, Aaron Rainbolt wrote:
> 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?

Does your BIOS offer any options for these?

Intel(R) SpeedStep(TM)
Intel Speed Shift Technology(TM)

I believe you need those enabled for this to work properly.