[PATCH 19/29] x86, tsx: Add support for rwsem elision

Andi Kleen
2013-03-23T01:27:06Z

Add the standard elide wrapper macros to rwsems to enable
lock elision for rwsems. Main target is mmap_sem.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/include/asm/rwsem.h | 23 ++++++++++++++++++++++-
arch/x86/kernel/rtm-locks.c | 3 +++
include/linux/rwsem.h | 3 +++
3 files changed, 28 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index 2dbe4a7..f9297af 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -38,6 +38,7 @@

#ifdef __KERNEL__
#include <asm/asm.h>
+#include <linux/elide.h>

/*
* The bias values and the counter type limits the number of
@@ -57,11 +58,15 @@
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)

+extern bool rwsem_elision;
+
/*
* lock for reading
*/
static inline void __down_read(struct rw_semaphore *sem)
{
+ if (elide_lock(rwsem_elision, sem->count == 0))
+ return;
asm volatile("# beginning down_read\n\t"
LOCK_PREFIX _ASM_INC "(%1)\n\t"
/* adds 0x00000001 */
@@ -80,6 +85,9 @@ static inline void __down_read(struct rw_semaphore *sem)
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
long result, tmp;
+
+ if (elide_lock(rwsem_elision, sem->count == 0))
+ return 1;
asm volatile("# beginning __down_read_trylock\n\t"
" mov %0,%1\n\t"
"1:\n\t"
@@ -102,6 +110,9 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
long tmp;
+
+ if (elide_lock(rwsem_elision, sem->count == 0))
+ return;
asm volatile("# beginning down_write\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
/* adds 0xffff0001, returns the old value */
@@ -126,7 +137,11 @@ static inline void __down_write(struct rw_semaphore *sem)
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
- long ret = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
+ long ret;
+
+ if (elide_lock(rwsem_elision, sem->count == 0))
+ return 1;
+ ret = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
if (ret == RWSEM_UNLOCKED_VALUE)
return 1;
@@ -139,6 +154,9 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
static inline void __up_read(struct rw_semaphore *sem)
{
long tmp;
+
+ if (elide_unlock(sem->count == 0))
+ return;
asm volatile("# beginning __up_read\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
/* subtracts 1, returns the old value */
@@ -157,6 +175,9 @@ static inline void __up_read(struct rw_semaphore *sem)
static inline void __up_write(struct rw_semaphore *sem)
{
long tmp;
+
+ if (elide_unlock(sem->count == 0))
+ return;
asm volatile("# beginning __up_write\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
/* subtracts 0xffff0001, returns the old value */
diff --git a/arch/x86/kernel/rtm-locks.c b/arch/x86/kernel/rtm-locks.c
index f3ae8e6..1811028 100644
--- a/arch/x86/kernel/rtm-locks.c
+++ b/arch/x86/kernel/rtm-locks.c
@@ -351,3 +351,6 @@ void init_rtm_spinlocks(void)

__read_mostly bool mutex_elision = true;
module_param(mutex_elision, bool, 0644);
+
+__read_mostly bool rwsem_elision = true;
+module_param(rwsem_elision, bool, 0644);
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 8da67d6..436e430 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -16,6 +16,8 @@

#include <linux/atomic.h>

+#include <linux/elide.h>
+
struct rw_semaphore;

#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
@@ -42,6 +44,7 @@ extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
+ elide_abort();
return sem->count != 0;
}

--
1.7.7.6