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!"
On Thu, 23 Nov 2006 18:48:52 +0530
Gautham R Shenoy <[email protected]> wrote:
> 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 ;-)
hm.
> 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)
> +
But what to do about the now-unneeded mutex?
We can just leave it there if CONFIG_HOTPLUG_CPU=n but then we'll get
unused variable warnings for statically-defined mutexes.
To fix that would require either
#ifdef CONFIG_HOTPLUG_CPU
#define DEFINE_MUTEX_HOTPLUG_CPU(m) DEFINE_MUTEX(m)
#else
#define DEFINE_MUTEX_HOTPLUG_CPU(m)
#endif
or
#define cpuhotplug_mutex_lock(m) do { (void)(m); } while (0)
Given that the former won't work, I'd suggest the latter ;)
Hi Andrew,
> >
> > 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 +++++++++++++++
[snip]
> > 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)
> > +
>
> But what to do about the now-unneeded mutex?
>
> We can just leave it there if CONFIG_HOTPLUG_CPU=n but then we'll get
> unused variable warnings for statically-defined mutexes.
Why even leave it there?
Can't we do something as follows, which has already been suggested in
the patch description:
Each hotcpu aware subsystem defines the hotcpu_mutex as follows
#ifdef CONFIG_HOTPLUG_CPU
[static] DEFINE_MUTEX(my_hotcpu_mutex);
#endif
That way, we won't be having any unneeded mutexes at all.
> To fix that would require either
>
> #ifdef CONFIG_HOTPLUG_CPU
> #define DEFINE_MUTEX_HOTPLUG_CPU(m) DEFINE_MUTEX(m)
> #else
> #define DEFINE_MUTEX_HOTPLUG_CPU(m)
> #endif
>
Yup, this won't work. Wish we could cook up something like this, but
alas! Most of these mutexes are defined with the static keyword,
which causes compile errors with CONFIG_HOTPLUG_CPU=n.
> or
>
> #define cpuhotplug_mutex_lock(m) do { (void)(m); } while (0)
>
>
> Given that the former won't work, I'd suggest the latter ;)
>
regards
gautham.
--
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!"
On Fri, Nov 24, 2006 at 09:57:02AM +0530, Gautham R Shenoy wrote:
> > But what to do about the now-unneeded mutex?
> >
> > We can just leave it there if CONFIG_HOTPLUG_CPU=n but then we'll get
> > unused variable warnings for statically-defined mutexes.
>
> Why even leave it there?
>
> Can't we do something as follows, which has already been suggested in
> the patch description:
>
> Each hotcpu aware subsystem defines the hotcpu_mutex as follows
> #ifdef CONFIG_HOTPLUG_CPU
> [static] DEFINE_MUTEX(my_hotcpu_mutex);
> #endif
>
> That way, we won't be having any unneeded mutexes at all.
I take back these words. In addition to the fact that this would
introduce more #ifdef noise in .c files, this approach won't work
in cases where we will be reusing existing mutexes as hotcpu_mutexes.
Eg: workqueue_mutex in kernel/workqueue.c and cache_chain_mutex in
mm/slab.c
> > or
> >
> > #define cpuhotplug_mutex_lock(m) do { (void)(m); } while (0)
> >
> >
> > Given that the former won't work, I'd suggest the latter ;)
The patch below implements the latter :)
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.
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 { (void)(m); } while (0)
+#define cpuhotplug_mutex_unlock(m) do { (void)(m); } 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!"