On Sat, 12 May 2007 11:06:24 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:
Like this:
From: Andrew Morton <akpm@linux-foundation.org>
per-cpu counters presently must iterate over all possible CPUs in the
exhaustive percpu_counter_sum().
But it can be much better to only iterate over the presently-online CPUs. To
do this, we must arrange for an offlined CPU's count to be spilled into the
counter's central count.
We can do this for all percpu_counters in the machine by linking them into a
single global list and walking that list at CPU_DEAD time.
(I hope. Might have race windows in which the percpu_counter_sum() count is
inaccurate?)
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/percpu_counter.h | 18 ++------
lib/percpu_counter.c | 66 +++++++++++++++++++++++++++++++
2 files changed, 72 insertions(+), 12 deletions(-)
diff -puN lib/percpu_counter.c~percpu_counters-use-cpu-notifiers lib/percpu_counter.c
--- a/lib/percpu_counter.c~percpu_counters-use-cpu-notifiers
+++ a/lib/percpu_counter.c
@@ -3,8 +3,17 @@
*/
#include <linux/percpu_counter.h>
+#include <linux/notifier.h>
+#include <linux/mutex.h>
+#include <linux/init.h>
+#include <linux/cpu.h>
#include <linux/module.h>
+#ifdef CONFIG_HOTPLUG_CPU
+static LIST_HEAD(percpu_counters);
+static DEFINE_MUTEX(percpu_counters_lock);
+#endif
+
void percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
{
long count;
@@ -44,3 +53,60 @@ s64 percpu_counter_sum(struct percpu_cou
return ret < 0 ? 0 : ret;
}
EXPORT_SYMBOL(percpu_counter_sum);
+
+void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
+{
+ spin_lock_init(&fbc->lock);
+ fbc->count = amount;
+ fbc->counters = alloc_percpu(s32);
+#ifdef CONFIG_HOTPLUG_CPU
+ mutex_lock(&percpu_counters_lock);
+ list_add(&fbc->list, &percpu_counters);
+ mutex_unlock(&percpu_counters_lock);
+#endif
+}
+EXPORT_SYMBOL(percpu_counter_init);
+
+void percpu_counter_destroy(struct percpu_counter *fbc)
+{
+ free_percpu(fbc->counters);
+#ifdef CONFIG_HOTPLUG_CPU
+ mutex_lock(&percpu_counters_lock);
+ list_del(&fbc->list);
+ mutex_unlock(&percpu_counters_lock);
+#endif
+}
+EXPORT_SYMBOL(percpu_counter_destroy);
+
+#ifdef CONFIG_HOTPLUG_CPU
+static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
+ unsigned long action, void *hcpu)
+{
+ unsigned int cpu;
+ struct percpu_counter *fbc;
+
+ if (action != CPU_DEAD)
+ return NOTIFY_OK;
+
+ cpu = (unsigned long)hcpu;
+ mutex_lock(&percpu_counters_lock);
+ list_for_each_entry(fbc, &percpu_counters, list) {
+ s32 *pcount;
+
+ spin_lock(&fbc->lock);
+ pcount = per_cpu_ptr(fbc->counters, cpu);
+ fbc->count += *pcount;
+ *pcount = 0;
+ spin_unlock(&fbc->lock);
+ }
+ mutex_unlock(&percpu_counters_lock);
+ return NOTIFY_OK;
+}
+
+static int __init percpu_counter_startup(void)
+{
+ hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
+ return 0;
+}
+module_init(percpu_counter_startup);
+#endif
diff -puN include/linux/percpu.h~percpu_counters-use-cpu-notifiers include/linux/percpu.h
diff -puN include/linux/percpu_counter.h~percpu_counters-use-cpu-notifiers include/linux/percpu_counter.h
--- a/include/linux/percpu_counter.h~percpu_counters-use-cpu-notifiers
+++ a/include/linux/percpu_counter.h
@@ -8,6 +8,7 @@
#include <linux/spinlock.h>
#include <linux/smp.h>
+#include <linux/list.h>
#include <linux/threads.h>
#include <linux/percpu.h>
#include <linux/types.h>
@@ -17,6 +18,9 @@
struct percpu_counter {
spinlock_t lock;
s64 count;
+#ifdef CONFIG_HOTPLUG_CPU
+ struct list_head list; /* All percpu_counters are on a list */
+#endif
s32 *counters;
};
@@ -26,18 +30,8 @@ struct percpu_counter {
#define FBC_BATCH (NR_CPUS*4)
#endif
-static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
-{
- spin_lock_init(&fbc->lock);
- fbc->count = amount;
- fbc->counters = alloc_percpu(s32);
-}
-
-static inline void percpu_counter_destroy(struct percpu_counter *fbc)
-{
- free_percpu(fbc->counters);
-}
-
+void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
+void percpu_counter_destroy(struct percpu_counter *fbc);
void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
s64 percpu_counter_sum(struct percpu_counter *fbc);
_
and then this:
From: Andrew Morton <akpm@linux-foundation.org>
Now that we have implemented hotunplug-time counter spilling,
percpu_counter_sum() only needs to look at online CPus.
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
lib/percpu_counter.c | 2 +-
1 files changed, 1 insertion(+), 1 deletion(-)
diff -puN lib/percpu_counter.c~percpu_counters-use-for_each_online_cpu lib/percpu_counter.c
--- a/lib/percpu_counter.c~percpu_counters-use-for_each_online_cpu
+++ a/lib/percpu_counter.c
@@ -45,7 +45,7 @@ s64 percpu_counter_sum(struct percpu_cou
spin_lock(&fbc->lock);
ret = fbc->count;
- for_each_possible_cpu(cpu) {
+ for_each_online_cpu(cpu) {
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
ret += *pcount;
}
_
-
