Per-CPU rwlocks ought to give better performance than global rwlocks.
That is where the "per-CPU" component comes in. So introduce the necessary
per-CPU variables that would be necessary at the reader and the writer sides,
and add the support for dynamically initializing per-CPU rwlocks.
These per-CPU variables will be used subsequently to implement the core
algorithm behind per-CPU rwlocks.
Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---
include/linux/percpu-rwlock.h | 4 ++++
lib/percpu-rwlock.c | 21 +++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/include/linux/percpu-rwlock.h b/include/linux/percpu-rwlock.h
index 45620d0..cd5eab5 100644
--- a/include/linux/percpu-rwlock.h
+++ b/include/linux/percpu-rwlock.h
@@ -29,6 +29,8 @@
#include <linux/spinlock.h>
struct percpu_rwlock {
+ unsigned long __percpu *reader_refcnt;
+ bool __percpu *writer_signal;
rwlock_t global_rwlock;
};
@@ -41,6 +43,8 @@ extern void percpu_write_unlock(struct percpu_rwlock *);
extern int __percpu_init_rwlock(struct percpu_rwlock *,
const char *, struct lock_class_key *);
+extern void percpu_free_rwlock(struct percpu_rwlock *);
+
#define percpu_init_rwlock(pcpu_rwlock) \
({ static struct lock_class_key rwlock_key; \
__percpu_init_rwlock(pcpu_rwlock, #pcpu_rwlock, &rwlock_key); \
diff --git a/lib/percpu-rwlock.c b/lib/percpu-rwlock.c
index af0c714..80dad93 100644
--- a/lib/percpu-rwlock.c
+++ b/lib/percpu-rwlock.c
@@ -31,6 +31,17 @@
int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock,
const char *name, struct lock_class_key *rwlock_key)
{
+ pcpu_rwlock->reader_refcnt = alloc_percpu(unsigned long);
+ if (unlikely(!pcpu_rwlock->reader_refcnt))
+ return -ENOMEM;
+
+ pcpu_rwlock->writer_signal = alloc_percpu(bool);
+ if (unlikely(!pcpu_rwlock->writer_signal)) {
+ free_percpu(pcpu_rwlock->reader_refcnt);
+ pcpu_rwlock->reader_refcnt = NULL;
+ return -ENOMEM;
+ }
+
/* ->global_rwlock represents the whole percpu_rwlock for lockdep */
#ifdef CONFIG_DEBUG_SPINLOCK
__rwlock_init(&pcpu_rwlock->global_rwlock, name, rwlock_key);
@@ -41,6 +52,16 @@ int __percpu_init_rwlock(struct percpu_rwlock *pcpu_rwlock,
return 0;
}
+void percpu_free_rwlock(struct percpu_rwlock *pcpu_rwlock)
+{
+ free_percpu(pcpu_rwlock->reader_refcnt);
+ free_percpu(pcpu_rwlock->writer_signal);
+
+ /* Catch use-after-free bugs */
+ pcpu_rwlock->reader_refcnt = NULL;
+ pcpu_rwlock->writer_signal = NULL;
+}
+
void percpu_read_lock(struct percpu_rwlock *pcpu_rwlock)
{
read_lock(&pcpu_rwlock->global_rwlock);
--
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