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[PATCH v4] x86/cpufreq: Add Kconfig option for CPU frequency scaling

  • To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Stefano Stabellini <stefano.stabellini@xxxxxxx>
  • Date: Fri, 13 Feb 2026 15:51:02 -0800
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  • Cc: <jbeulich@xxxxxxxx>, <andrew.cooper3@xxxxxxxxxx>, <roger.pau@xxxxxxxxxx>, <jason.andryuk@xxxxxxx>, <stefano.stabellini@xxxxxxx>, <alejandro.garciavallejo@xxxxxxx>
  • Delivery-date: Fri, 13 Feb 2026 23:51:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Add CONFIG_CPUFREQ to allow CPU frequency scaling support to be
disabled at build time. When disabled, this removes cpufreq code
from the build.

Introduce IS_ENABLED(CONFIG_CPUFREQ) checks for relevant do_pm_op and
do_platform_op subops and other functions that require CONFIG_CPUFREQ to
work.

Add stubs where necessary.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
---
Changes in v4:
- fix IS_ENABLED(CPUFREQ)
- remove #ifdef in platform_hypercall.c and use DCE
- move cpufreq_controller enum out of #ifdef
---
 xen/arch/x86/acpi/Makefile                |  2 +-
 xen/arch/x86/platform_hypercall.c         |  6 ++++--
 xen/drivers/Makefile                      |  2 +-
 xen/drivers/acpi/pm-op.c                  |  3 ++-
 xen/drivers/acpi/pmstat.c                 |  8 ++++++--
 xen/drivers/cpufreq/Kconfig               | 14 +++++++++++++-
 xen/include/acpi/cpufreq/cpufreq.h        | 13 ++++++++++++-
 xen/include/acpi/cpufreq/processor_perf.h |  3 ---
 xen/include/xen/acpi.h                    |  8 ++++++++
 xen/include/xen/pmstat.h                  | 15 ++++++++++++++-
 xen/include/xen/sched.h                   |  7 +++++++
 11 files changed, 68 insertions(+), 13 deletions(-)

diff --git a/xen/arch/x86/acpi/Makefile b/xen/arch/x86/acpi/Makefile
index 041377e2bb..aa476f65d5 100644
--- a/xen/arch/x86/acpi/Makefile
+++ b/xen/arch/x86/acpi/Makefile
@@ -1,4 +1,4 @@
-obj-y += cpufreq/
+obj-$(CONFIG_CPUFREQ) += cpufreq/
 
 obj-y += lib.o power.o cpu_idle.o cpuidle_menu.o
 obj-bin-y += boot.init.o wakeup_prot.o
diff --git a/xen/arch/x86/platform_hypercall.c 
b/xen/arch/x86/platform_hypercall.c
index c6c5135806..1dc7dae919 100644
--- a/xen/arch/x86/platform_hypercall.c
+++ b/xen/arch/x86/platform_hypercall.c
@@ -487,7 +487,8 @@ ret_t do_platform_op(
 
     case XENPF_change_freq:
         ret = -ENOSYS;
-        if ( cpufreq_controller != FREQCTL_dom0_kernel )
+        if ( !IS_ENABLED(CONFIG_CPUFREQ) ||
+             cpufreq_controller != FREQCTL_dom0_kernel )
             break;
         ret = -EINVAL;
         if ( op->u.change_freq.flags || !cpu_online(op->u.change_freq.cpu) )
@@ -507,7 +508,8 @@ ret_t do_platform_op(
         XEN_GUEST_HANDLE(uint64) idletimes;
 
         ret = -ENOSYS;
-        if ( cpufreq_controller != FREQCTL_dom0_kernel )
+        if ( !IS_ENABLED(CONFIG_CPUFREQ) ||
+             cpufreq_controller != FREQCTL_dom0_kernel )
             break;
 
         ctlmap.nr_bits  = op->u.getidletime.cpumap_nr_cpus;
diff --git a/xen/drivers/Makefile b/xen/drivers/Makefile
index 2a1ae8ad13..3d81b8dde4 100644
--- a/xen/drivers/Makefile
+++ b/xen/drivers/Makefile
@@ -1,5 +1,5 @@
 obj-y += char/
-obj-$(CONFIG_HAS_CPUFREQ) += cpufreq/
+obj-$(CONFIG_CPUFREQ) += cpufreq/
 obj-$(CONFIG_HAS_PCI) += pci/
 obj-$(CONFIG_HAS_VPCI) += vpci/
 obj-$(CONFIG_HAS_PASSTHROUGH) += passthrough/
diff --git a/xen/drivers/acpi/pm-op.c b/xen/drivers/acpi/pm-op.c
index 07bddc58d9..72f1eea62f 100644
--- a/xen/drivers/acpi/pm-op.c
+++ b/xen/drivers/acpi/pm-op.c
@@ -367,7 +367,8 @@ int do_pm_op(struct xen_sysctl_pm_op *op)
         return ret;
     }
 
-    if ( op->cpuid >= nr_cpu_ids || !cpu_online(op->cpuid) )
+    if ( op->cpuid >= nr_cpu_ids || !cpu_online(op->cpuid) ||
+         !IS_ENABLED(CONFIG_CPUFREQ) )
         return -EINVAL;
     pmpt = processor_pminfo[op->cpuid];
 
diff --git a/xen/drivers/acpi/pmstat.c b/xen/drivers/acpi/pmstat.c
index 0f31736df2..d640d3a92c 100644
--- a/xen/drivers/acpi/pmstat.c
+++ b/xen/drivers/acpi/pmstat.c
@@ -76,6 +76,9 @@ void cpufreq_statistic_update(unsigned int cpu, uint8_t from, 
uint8_t to)
     spinlock_t *cpufreq_statistic_lock =
                &per_cpu(cpufreq_statistic_lock, cpu);
 
+    if ( !IS_ENABLED(CONFIG_CPUFREQ) )
+        return;
+
     spin_lock(cpufreq_statistic_lock);
 
     pxpt = per_cpu(cpufreq_statistic_data, cpu);
@@ -105,7 +108,7 @@ int cpufreq_statistic_init(unsigned int cpu)
 
     spin_lock_init(cpufreq_statistic_lock);
 
-    if ( !pmpt )
+    if ( !pmpt || !IS_ENABLED(CONFIG_CPUFREQ) )
         return -EINVAL;
 
     /* Only need to initialize in Px mode */
@@ -225,7 +228,8 @@ int do_get_pm_info(struct xen_sysctl_get_pmstat *op)
     int ret = 0;
     const struct processor_pminfo *pmpt;
 
-    if ( !op || (op->cpuid >= nr_cpu_ids) || !cpu_online(op->cpuid) )
+    if ( !IS_ENABLED(CONFIG_CPUFREQ) || !op || (op->cpuid >= nr_cpu_ids) ||
+         !cpu_online(op->cpuid) )
         return -EINVAL;
     pmpt = processor_pminfo[op->cpuid];
 
diff --git a/xen/drivers/cpufreq/Kconfig b/xen/drivers/cpufreq/Kconfig
index cce80f4aec..b9b93c1a26 100644
--- a/xen/drivers/cpufreq/Kconfig
+++ b/xen/drivers/cpufreq/Kconfig
@@ -1,3 +1,15 @@
-
 config HAS_CPUFREQ
        bool
+
+config CPUFREQ
+       bool "CPU Frequency scaling"
+       default y
+       depends on HAS_CPUFREQ
+       help
+         Enable CPU frequency scaling and power management governors.
+         This allows Xen to dynamically adjust CPU P-states (performance
+         states) based on system load.
+
+         Disabling this option removes all cpufreq governors and power
+         management interfaces. This is useful for real-time systems or
+         minimal hypervisor builds.
diff --git a/xen/include/acpi/cpufreq/cpufreq.h 
b/xen/include/acpi/cpufreq/cpufreq.h
index 0171ccf0ba..828d23961c 100644
--- a/xen/include/acpi/cpufreq/cpufreq.h
+++ b/xen/include/acpi/cpufreq/cpufreq.h
@@ -381,8 +381,19 @@ int write_ondemand_up_threshold(unsigned int up_threshold);
 
 int write_userspace_scaling_setspeed(unsigned int cpu, unsigned int freq);
 
+#ifdef CONFIG_CPUFREQ
+int cpufreq_add_cpu(unsigned int cpu);
+int cpufreq_del_cpu(unsigned int cpu);
+
 void cpufreq_dbs_timer_suspend(void);
 void cpufreq_dbs_timer_resume(void);
+#else
+static inline int cpufreq_add_cpu(unsigned int cpu) { return -EOPNOTSUPP; }
+static inline int cpufreq_del_cpu(unsigned int cpu) { return -EOPNOTSUPP; }
+
+static inline void cpufreq_dbs_timer_suspend(void) {}
+static inline void cpufreq_dbs_timer_resume(void) {}
+#endif
 
 void intel_feature_detect(struct cpufreq_policy *policy);
 
@@ -398,7 +409,7 @@ void intel_feature_detect(struct cpufreq_policy *policy);
 
 int hwp_cmdline_parse(const char *s, const char *e);
 int hwp_register_driver(void);
-#ifdef CONFIG_INTEL
+#if defined(CONFIG_INTEL) && defined(CONFIG_CPUFREQ)
 bool hwp_active(void);
 #else
 static inline bool hwp_active(void) { return false; }
diff --git a/xen/include/acpi/cpufreq/processor_perf.h 
b/xen/include/acpi/cpufreq/processor_perf.h
index 0a87bc0384..bad9d94865 100644
--- a/xen/include/acpi/cpufreq/processor_perf.h
+++ b/xen/include/acpi/cpufreq/processor_perf.h
@@ -36,9 +36,6 @@ static inline void cpufreq_statistic_exit(unsigned int cpu) {}
 
 int  cpufreq_limit_change(unsigned int cpu);
 
-int  cpufreq_add_cpu(unsigned int cpu);
-int  cpufreq_del_cpu(unsigned int cpu);
-
 struct processor_performance {
     uint32_t state;
     uint32_t platform_limit;
diff --git a/xen/include/xen/acpi.h b/xen/include/xen/acpi.h
index 90635ba0f3..ae6dba481c 100644
--- a/xen/include/xen/acpi.h
+++ b/xen/include/xen/acpi.h
@@ -186,7 +186,15 @@ static inline void acpi_set_csubstate_limit(unsigned int 
new_limit) { return; }
 #endif
 
 #ifdef XEN_GUEST_HANDLE
+#ifdef CONFIG_CPUFREQ
 int acpi_set_pdc_bits(unsigned int acpi_id, XEN_GUEST_HANDLE(uint32));
+#else
+static inline int acpi_set_pdc_bits(unsigned int acpi_id,
+                                    XEN_GUEST_HANDLE(uint32) pdc)
+{
+    return -EOPNOTSUPP;
+}
+#endif
 #endif
 int arch_acpi_set_pdc_bits(u32 acpi_id, u32 *, u32 mask);
 
diff --git a/xen/include/xen/pmstat.h b/xen/include/xen/pmstat.h
index 6096560d3c..51d3ee404f 100644
--- a/xen/include/xen/pmstat.h
+++ b/xen/include/xen/pmstat.h
@@ -5,10 +5,23 @@
 #include <public/platform.h> /* for struct xen_processor_power */
 #include <public/sysctl.h>   /* for struct pm_cx_stat */
 
+#ifdef CONFIG_CPUFREQ
 int set_px_pminfo(uint32_t acpi_id, struct xen_processor_performance *perf);
-long set_cx_pminfo(uint32_t acpi_id, struct xen_processor_power *power);
 int set_cppc_pminfo(unsigned int acpi_id,
                     const struct xen_processor_cppc *cppc_data);
+#else
+static inline int set_px_pminfo(uint32_t acpi_id,
+                                struct xen_processor_performance *perf)
+{
+    return -EOPNOTSUPP;
+}
+static inline int set_cppc_pminfo(unsigned int acpi_id,
+                                  const struct xen_processor_cppc *cppc_data)
+{
+    return -EOPNOTSUPP;
+}
+#endif
+long set_cx_pminfo(uint32_t acpi_id, struct xen_processor_power *power);
 
 #ifdef CONFIG_COMPAT
 struct compat_processor_performance;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 1268632344..084f3835dc 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -1259,6 +1259,7 @@ extern enum cpufreq_controller {
     FREQCTL_none, FREQCTL_dom0_kernel, FREQCTL_xen
 } cpufreq_controller;
 
+#ifdef CONFIG_CPUFREQ
 static always_inline bool is_cpufreq_controller(const struct domain *d)
 {
     /*
@@ -1274,6 +1275,12 @@ static always_inline bool is_cpufreq_controller(const 
struct domain *d)
     return (is_pv_domain(d) && is_hardware_domain(d) &&
             cpufreq_controller == FREQCTL_dom0_kernel);
 }
+#else
+static always_inline bool is_cpufreq_controller(const struct domain *d)
+{
+    return false;
+}
+#endif
 
 int cpupool_move_domain(struct domain *d, struct cpupool *c);
 int cpupool_do_sysctl(struct xen_sysctl_cpupool_op *op);
-- 
2.25.1

 

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