linux-kernel - [PATCH] cpufreq: intel_pstate: Enable asym capacity only when cpu smt is not possible

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Message-Id: <20260128031521.389765-1-tianyaxiong@kylinos.cn>
Date: Wed, 28 Jan 2026 11:15:21 +0800
From: Yaxiong Tian <tianyaxiong@...inos.cn>
To: rafael@...nel.org,
	srinivas.pandruvada@...ux.intel.com,
	lenb@...nel.org,
	viresh.kumar@...aro.org,
	ricardo.neri-calderon@...ux.intel.com
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yaxiong Tian <tianyaxiong@...inos.cn>
Subject: [PATCH] cpufreq: intel_pstate: Enable asym capacity only when cpu smt is not possible

According to the description in the intel_pstate.rst documentation,
Capacity-Aware Scheduling and Energy-Aware Scheduling are only
supported on a hybrid processor without SMT. Previously, the system
used sched_smt_active() for judgment, which is not a strict condition
because users can switch it on or off via /sys at any time.

This could lead to incorrect driver settings in certain scenarios.
 For example, on a CPU that supports SMT, a user can disable SMT
via the nosmt parameter to enable asym capacity, and then re-enable
SMT via /sys. In such cases, some settings in the driver would no
longer be correct.

To address this issue, replace sched_smt_active() with cpu_smt_possible(),
and only enable asym capacity when cpu smt is not possible.

Fixes: 929ebc93ccaa ("cpufreq: intel_pstate: Set asymmetric CPU capacity on hybrid systems")
Signed-off-by: Yaxiong Tian <tianyaxiong@...inos.cn>
---
 drivers/cpufreq/intel_pstate.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index ec4abe374573..8105c41861a3 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1142,8 +1142,11 @@ static void hybrid_refresh_cpu_capacity_scaling(void)
 
 static void hybrid_init_cpu_capacity_scaling(bool refresh)
 {
-	/* Bail out if enabling capacity-aware scheduling is prohibited. */
-	if (no_cas)
+	/*
+	 * Bail out if capacity-aware scheduling is prohibited, or if SMT is
+	 * possible, as the capacity of SMT threads cannot be determined reliably.
+	 */
+	if (no_cas || cpu_smt_possible())
 		return;
 
 	/*
@@ -1156,12 +1159,8 @@ static void hybrid_init_cpu_capacity_scaling(bool refresh)
 		return;
 	}
 
-	/*
-	 * On hybrid systems, use asym capacity instead of ITMT, but because
-	 * the capacity of SMT threads is not deterministic even approximately,
-	 * do not do that when SMT is in use.
-	 */
-	if (hwp_is_hybrid && !sched_smt_active() && arch_enable_hybrid_capacity_scale()) {
+	/* On hybrid systems, use asym capacity instead of ITMT */
+	if (hwp_is_hybrid && arch_enable_hybrid_capacity_scale()) {
 		hybrid_refresh_cpu_capacity_scaling();
 		/*
 		 * Disabling ITMT causes sched domains to be rebuilt to disable asym
-- 
2.25.1