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authorAndrew Morton <akpm@linux-foundation.org>2007-07-15 23:39:51 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-16 09:05:41 -0700
commitc67ad917cbf21b2862e2cf8e8b28339872ef7927 (patch)
tree362d8cf8668998b8cd5deb611693f584b8df5ee5
parent85420ccad1610f123365eec89848ef25641bc6b7 (diff)
downloadop-kernel-dev-c67ad917cbf21b2862e2cf8e8b28339872ef7927.zip
op-kernel-dev-c67ad917cbf21b2862e2cf8e8b28339872ef7927.tar.gz
percpu_counters(): use cpu notifiers
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?) Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/percpu_counter.h18
-rw-r--r--lib/percpu_counter.c66
2 files changed, 72 insertions, 12 deletions
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index f5aa593..3d9f709 100644
--- a/include/linux/percpu_counter.h
+++ b/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);
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 8504490..8901c4e 100644
--- a/lib/percpu_counter.c
+++ b/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_counter *fbc)
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
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