cpu/hotplug: Create SMT sysfs interface for all arches

Make the /sys/devices/system/cpu/smt/* files available on all arches, so
user space has a consistent way to detect whether SMT is enabled.

The 'control' file now shows 'notimplemented' for architectures which
don't yet have CONFIG_HOTPLUG_SMT.

[ tglx: Make notimplemented a real state ]

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Link: https://lkml.kernel.org/r/469c2b98055f2c41e75748e06447d592a64080c9.1553635520.git.jpoimboe@redhat.com

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 9605dbd4b5b59ecc251913b1b327e6031cfb875f..5eea46fefcb2a95442f0fd77ce1b3bee07541821 100644 (file)
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -511,10 +511,12 @@ Description:      Control Symetric Multi Threading (SMT)
                control: Read/write interface to control SMT. Possible
                         values:
 
-                        "on"           SMT is enabled
-                        "off"          SMT is disabled
-                        "forceoff"     SMT is force disabled. Cannot be changed.
-                        "notsupported" SMT is not supported by the CPU
+                        "on"             SMT is enabled
+                        "off"            SMT is disabled
+                        "forceoff"       SMT is force disabled. Cannot be changed.
+                        "notsupported"   SMT is not supported by the CPU
+                        "notimplemented" SMT runtime toggling is not
+                                         implemented for the architecture
 
                         If control status is "forceoff" or "notsupported" writes
                         are rejected.

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 5041357d0297afdce8b5605970947b34f85e7205..ae99dde02320904e361629a30a4e01aae3553d6f 100644 (file)
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -175,6 +175,7 @@ enum cpuhp_smt_control {
        CPU_SMT_DISABLED,
        CPU_SMT_FORCE_DISABLED,
        CPU_SMT_NOT_SUPPORTED,
+       CPU_SMT_NOT_IMPLEMENTED,
 };
 
 #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT)
@@ -182,7 +183,7 @@ extern enum cpuhp_smt_control cpu_smt_control;
 extern void cpu_smt_disable(bool force);
 extern void cpu_smt_check_topology(void);
 #else
-# define cpu_smt_control               (CPU_SMT_ENABLED)
+# define cpu_smt_control               (CPU_SMT_NOT_IMPLEMENTED)
 static inline void cpu_smt_disable(bool force) { }
 static inline void cpu_smt_check_topology(void) { }
 #endif

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6754f3ecfd943c97af0b865197d01366abac7c73..b8bf3f93e39b739a63081a2a80198f164fd53d6a 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2033,19 +2033,6 @@ static const struct attribute_group cpuhp_cpu_root_attr_group = {
 
 #ifdef CONFIG_HOTPLUG_SMT
 
-static const char *smt_states[] = {
-       [CPU_SMT_ENABLED]               = "on",
-       [CPU_SMT_DISABLED]              = "off",
-       [CPU_SMT_FORCE_DISABLED]        = "forceoff",
-       [CPU_SMT_NOT_SUPPORTED]         = "notsupported",
-};
-
-static ssize_t
-show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
-{
-       return snprintf(buf, PAGE_SIZE - 2, "%s\n", smt_states[cpu_smt_control]);
-}
-
 static void cpuhp_offline_cpu_device(unsigned int cpu)
 {
        struct device *dev = get_cpu_device(cpu);
@@ -2116,9 +2103,10 @@ static int cpuhp_smt_enable(void)
        return ret;
 }
 
+
 static ssize_t
-store_smt_control(struct device *dev, struct device_attribute *attr,
-                 const char *buf, size_t count)
+__store_smt_control(struct device *dev, struct device_attribute *attr,
+                   const char *buf, size_t count)
 {
        int ctrlval, ret;
 
@@ -2156,14 +2144,44 @@ store_smt_control(struct device *dev, struct device_attribute *attr,
        unlock_device_hotplug();
        return ret ? ret : count;
 }
+
+#else /* !CONFIG_HOTPLUG_SMT */
+static ssize_t
+__store_smt_control(struct device *dev, struct device_attribute *attr,
+                   const char *buf, size_t count)
+{
+       return -ENODEV;
+}
+#endif /* CONFIG_HOTPLUG_SMT */
+
+static const char *smt_states[] = {
+       [CPU_SMT_ENABLED]               = "on",
+       [CPU_SMT_DISABLED]              = "off",
+       [CPU_SMT_FORCE_DISABLED]        = "forceoff",
+       [CPU_SMT_NOT_SUPPORTED]         = "notsupported",
+       [CPU_SMT_NOT_IMPLEMENTED]       = "notimplemented",
+};
+
+static ssize_t
+show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
+{
+       const char *state = smt_states[cpu_smt_control];
+
+       return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
+}
+
+static ssize_t
+store_smt_control(struct device *dev, struct device_attribute *attr,
+                 const char *buf, size_t count)
+{
+       return __store_smt_control(dev, attr, buf, count);
+}
 static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);
 
 static ssize_t
 show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
 {
-       bool active = topology_max_smt_threads() > 1;
-
-       return snprintf(buf, PAGE_SIZE - 2, "%d\n", active);
+       return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
 }
 static DEVICE_ATTR(active, 0444, show_smt_active, NULL);
 
@@ -2179,21 +2197,17 @@ static const struct attribute_group cpuhp_smt_attr_group = {
        NULL
 };
 
-static int __init cpu_smt_state_init(void)
+static int __init cpu_smt_sysfs_init(void)
 {
        return sysfs_create_group(&cpu_subsys.dev_root->kobj,
                                  &cpuhp_smt_attr_group);
 }
 
-#else
-static inline int cpu_smt_state_init(void) { return 0; }
-#endif
-
 static int __init cpuhp_sysfs_init(void)
 {
        int cpu, ret;
 
-       ret = cpu_smt_state_init();
+       ret = cpu_smt_sysfs_init();
        if (ret)
                return ret;
 
@@ -2214,7 +2228,7 @@ static int __init cpuhp_sysfs_init(void)
        return 0;
 }
 device_initcall(cpuhp_sysfs_init);
-#endif
+#endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */
 
 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that