linux-kernel - Re: [PATCH 0/4] ACPI: CPPC: Fixes to limit actions to online CPUs

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Message-ID: <CAM+eXpe1j5=PW9AuJCJQWat=ivwViU45y0ortdiav-kX=2Hs+g@mail.gmail.com>
Date: Wed, 5 Nov 2025 13:13:08 -0800
From: Chris H <chris.harris79@...il.com>
To: "Gautham R. Shenoy" <gautham.shenoy@....com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	Mario Limonciello <mario.limonciello@....com>, Yunhui Cui <cuiyunhui@...edance.com>, 
	Jeremy Linton <jeremy.linton@....com>, Viresh Kumar <viresh.kumar@...aro.org>, 
	Ionela Voinescu <ionela.voinescu@....com>, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 0/4] ACPI: CPPC: Fixes to limit actions to online CPUs

Confirming: I've tested the first two patches in the series on kernel
v6.17.  The patches successfully resolve the issue described, allowing
one to boot with amd-pstate + nosmt=force.  In other words: receive
the expected amd-pstate scaling driver when SMT logical cores are
disabled.

ACPI: CPPC: Detect preferred core availability on online CPUs
ACPI: CPPC: Check _CPC validity for only the online CPUs

Thank you Mario and Gautham for addressing this so quickly.

Chris Harris

On Wed, Nov 5, 2025 at 6:39 AM Gautham R. Shenoy <gautham.shenoy@....com> wrote:
>
> Hello,
>
> Christopher Harris reported a regression between v6.10 to v6.11 that
> the amd-pstate driver failed to load even when the commandline had
> "amd_pstate=passive"
> (https://lore.kernel.org/lkml/CAM+eXpdDT7KjLV0AxEwOLkSJ2QtrsvGvjA2cCHvt1d0k2_C4Cw@mail.gmail.com/)
>
> On debugging the issue it was observed that when the commandline
> contains "nosmt=force", the CPPC code fails when performing certain
> checks such as checking for the presence of preferred cores and
> validity of the _CPC object since it iterates through all "present"
> CPUs while the object state was populated only for "online" CPUs.
>
> This patchset contains fixes to address this issue.
>
> The first two patches in the series address the issue reported by
> Chris.
>
> Patches 3 and 4 harden the code in a couple of more functions which
> iterated through the present CPUs when it is more apt to restrict the
> operations to online CPUs
>
>
>
> Gautham R. Shenoy (4):
>   ACPI: CPPC: Detect preferred core availability on online CPUs
>   ACPI: CPPC: Check _CPC validity for only the online CPUs
>   ACPI: CPPC: Perform fast check switch only for online CPUs
>   ACPI: CPPC: Limit perf ctrs in PCC check only to online CPUs
>
>  arch/x86/kernel/acpi/cppc.c | 2 +-
>  drivers/acpi/cppc_acpi.c    | 6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> --
> 2.34.1
>