When CONFIG_HOTPLUG_CPU is not set, lock_cpu_hotplug() and
unlock_cpu_hotplug() default to no-ops.
However, in case of the proposed per-subsystem hotcpu mutex scheme,
the hotcpu mutexes will be taken/released, even when
CONFIG_HOTPLUG_CPU is not set. This is an unnecessary overhead
both w.r.t space and time ;-)
This patch
* Provides a common interface for all the subsystems to lock and
unlock their per-subsystem hotcpu mutexes.
When CONFIG_HOTPLUG_CPU is not set, these operations would be no-ops.
Usage:
a) Each hotcpu aware subsystem defines the hotcpu_mutex as follows
#ifdef CONFIG_HOTPLUG_CPU
DEFINE_MUTEX(my_hotcpu_mutex);
#endif
b) The hotcpu aware subsystem uses
cpuhotplug_mutex_lock(&my_hotcpu_mutex)
and
cpuhotplug_mutex_unlock(&my_hotcpu_mutex)
instead of the usual mutex_lock/mutex_unlock.
Signed-off-by: Gautham R Shenoy <[email protected]>
---
include/linux/cpu.h | 15 +++++++++++++++
1 files changed, 15 insertions(+)
Index: hotplug/include/linux/cpu.h
===================================================================
--- hotplug.orig/include/linux/cpu.h
+++ hotplug/include/linux/cpu.h
@@ -24,6 +24,7 @@
#include <linux/compiler.h>
#include <linux/cpumask.h>
#include <asm/semaphore.h>
+#include <linux/mutex.h>
struct cpu {
int node_id; /* The node which contains the CPU */
@@ -74,6 +75,17 @@ extern struct sysdev_class cpu_sysdev_cl
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */
+
+static inline void cpuhotplug_mutex_lock(struct mutex *cpu_hp_mutex)
+{
+ mutex_lock(cpu_hp_mutex);
+}
+
+static inline void cpuhotplug_mutex_unlock(struct mutex *cpu_hp_mutex)
+{
+ mutex_unlock(cpu_hp_mutex);
+}
+
extern void lock_cpu_hotplug(void);
extern void unlock_cpu_hotplug(void);
#define hotcpu_notifier(fn, pri) { \
@@ -86,6 +98,9 @@ extern void unlock_cpu_hotplug(void);
int cpu_down(unsigned int cpu);
#define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
#else
+#define cpuhotplug_mutex_lock(m) do { } while (0)
+#define cpuhotplug_mutex_unlock(m) do { } while (0)
+
#define lock_cpu_hotplug() do { } while (0)
#define unlock_cpu_hotplug() do { } while (0)
#define lock_cpu_hotplug_interruptible() 0
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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