linux-kernel - [PATCH 1/4] ACPI: CPPC: Detect preferred core availability on online CPUs

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Message-ID: <20251105143851.4251-2-gautham.shenoy@amd.com>
Date: Wed, 5 Nov 2025 20:08:48 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: "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>
CC: <linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Christopher
 Harris" <chris.harris79@...il.com>, <linux-pm@...r.kernel.org>, "Gautham R.
 Shenoy" <gautham.shenoy@....com>
Subject: [PATCH 1/4] ACPI: CPPC: Detect preferred core availability on online CPUs

Commit 279f838a61f9 ("x86/amd: Detect preferred cores in
amd_get_boost_ratio_numerator()") introduced the ability to detect the
preferred core on AMD platforms by checking if there at least two
distinct highest_perf values.

However, it uses for_each_present_cpu() to iterate through all the
CPUs in the platform, which is problematic when the kernel is booted
with "nosmt=force" commandline option.

Hence limit the search to only the online CPUs.

Fixes: 279f838a61f9 ("x86/amd: Detect preferred cores in amd_get_boost_ratio_numerator()")
Reported-by: Christopher Harris <chris.harris79@...il.com>
Closes: https://lore.kernel.org/lkml/CAM+eXpdDT7KjLV0AxEwOLkSJ2QtrsvGvjA2cCHvt1d0k2_C4Cw@mail.gmail.com/
Signed-off-by: Gautham R. Shenoy <gautham.shenoy@....com>
---
 arch/x86/kernel/acpi/cppc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index 7047124490f6..d7c8ef1e354d 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -196,7 +196,7 @@ int amd_detect_prefcore(bool *detected)
 		break;
 	}
 
-	for_each_present_cpu(cpu) {
+	for_each_online_cpu(cpu) {
 		u32 tmp;
 		int ret;
 
-- 
2.34.1