lkml.org 
[lkml]   [2019]   [Mar]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2] cpu/hotplug: Create SMT sysfs interface for all arches
Date
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.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
v2: add "notimplemented" pseudo-state [tglx]

.../ABI/testing/sysfs-devices-system-cpu | 10 +--
include/linux/cpu.h | 2 +-
kernel/cpu.c | 72 +++++++++++--------
3 files changed, 51 insertions(+), 33 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 9605dbd4b5b5..5eea46fefcb2 100644
--- 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 5041357d0297..296753249343 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -182,7 +182,7 @@ 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_SUPPORTED)
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 f69ba38573c2..b0614263963b 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2019,19 +2019,6 @@ 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);
@@ -2102,9 +2089,10 @@ 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;

@@ -2120,9 +2108,6 @@ store_smt_control(struct device *dev, struct device_attribute *attr,
if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
return -EPERM;

- if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
- return -ENODEV;
-
ret = lock_device_hotplug_sysfs();
if (ret)
return ret;
@@ -2142,14 +2127,49 @@ 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 0;
+}
+#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",
+};
+
+static ssize_t
+show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ const char *state = IS_ENABLED(CONFIG_HOTPLUG_SMT) ?
+ smt_states[cpu_smt_control] :
+ "notimplemented";
+
+ 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)
+{
+
+ if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+ return -ENODEV;
+
+ 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);

@@ -2165,21 +2185,17 @@ 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;

@@ -2200,7 +2216,7 @@ 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
--
2.17.2
\
 
 \ /
  Last update: 2019-03-27 13:01    [W:0.041 / U:18.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site