svn commit: r234937 - in stable/8: lib/libthr/thread sys/kern
sys/sys
David Xu
davidxu at FreeBSD.org
Thu May 3 03:05:19 UTC 2012
Author: davidxu
Date: Thu May 3 03:05:18 2012
New Revision: 234937
URL: http://svn.freebsd.org/changeset/base/234937
Log:
Merge 233103, 233912 from head:
233103:
Some software think a mutex can be destroyed after it owned it, for
example, it uses a serialization point like following:
pthread_mutex_lock(&mutex);
pthread_mutex_unlock(&mutex);
pthread_mutex_destroy(&muetx);
They think a previous lock holder should have already left the mutex and
is no longer referencing it, so they destroy it. To be maximum compatible
with such code, we use IA64 version to unlock the mutex in kernel, remove
the two steps unlocking code.
233912:
umtx operation UMTX_OP_MUTEX_WAKE has a side-effect that it accesses
a mutex after a thread has unlocked it, it event writes data to the mutex
memory to clear contention bit, there is a race that other threads
can lock it and unlock it, then destroy it, so it should not write
data to the mutex memory if there isn't any waiter.
The new operation UMTX_OP_MUTEX_WAKE2 try to fix the problem. It
requires thread library to clear the lock word entirely, then
call the WAKE2 operation to check if there is any waiter in kernel,
and try to wake up a thread, if necessary, the contention bit is set again
by the operation. This also mitgates the chance that other threads find
the contention bit and try to enter kernel to compete with each other
to wake up sleeping thread, this is unnecessary. With this change, the
mutex owner is no longer holding the mutex until it reaches a point
where kernel umtx queue is locked, it releases the mutex as soon as
possible.
Performance is improved when the mutex is contensted heavily. On Intel
i3-2310M, the runtime of a benchmark program is reduced from 26.87 seconds
to 2.39 seconds, it even is better than UMTX_OP_MUTEX_WAKE which is
deprecated now. http://people.freebsd.org/~davidxu/bench/mutex_perf.c
Special code for stable/8:
And add code to detect if the UMTX_OP_MUTEX_WAKE2 is available.
PR: threads/167308
Modified:
stable/8/lib/libthr/thread/thr_private.h
stable/8/lib/libthr/thread/thr_umtx.c
stable/8/lib/libthr/thread/thr_umtx.h
stable/8/sys/kern/kern_umtx.c
stable/8/sys/sys/umtx.h
Directory Properties:
stable/8/lib/libthr/ (props changed)
Modified: stable/8/lib/libthr/thread/thr_private.h
==============================================================================
--- stable/8/lib/libthr/thread/thr_private.h Thu May 3 01:41:12 2012 (r234936)
+++ stable/8/lib/libthr/thread/thr_private.h Thu May 3 03:05:18 2012 (r234937)
@@ -706,8 +706,6 @@ ssize_t __sys_write(int, const void *, s
void __sys_exit(int);
#endif
-int _umtx_op_err(void *, int op, u_long, void *, void *) __hidden;
-
static inline int
_thr_isthreaded(void)
{
Modified: stable/8/lib/libthr/thread/thr_umtx.c
==============================================================================
--- stable/8/lib/libthr/thread/thr_umtx.c Thu May 3 01:41:12 2012 (r234936)
+++ stable/8/lib/libthr/thread/thr_umtx.c Thu May 3 03:05:18 2012 (r234937)
@@ -112,6 +112,35 @@ __thr_umutex_timedlock(struct umutex *mt
int
__thr_umutex_unlock(struct umutex *mtx, uint32_t id)
{
+ static int wake2_avail = 0;
+
+ if (__predict_false(wake2_avail == 0)) {
+ struct umutex test = DEFAULT_UMUTEX;
+
+ if (_umtx_op(&test, UMTX_OP_MUTEX_WAKE2, test.m_flags, 0, 0) == -1)
+ wake2_avail = -1;
+ else
+ wake2_avail = 1;
+ }
+
+ if (wake2_avail != 1)
+ goto unlock;
+
+ uint32_t flags = mtx->m_flags;
+
+ if ((flags & (UMUTEX_PRIO_PROTECT | UMUTEX_PRIO_INHERIT)) == 0) {
+ uint32_t owner;
+ do {
+ owner = mtx->m_owner;
+ if (__predict_false((owner & ~UMUTEX_CONTESTED) != id))
+ return (EPERM);
+ } while (__predict_false(!atomic_cmpset_rel_32(&mtx->m_owner,
+ owner, UMUTEX_UNOWNED)));
+ if ((owner & UMUTEX_CONTESTED))
+ (void)_umtx_op_err(mtx, UMTX_OP_MUTEX_WAKE2, flags, 0, 0);
+ return (0);
+ }
+unlock:
return _umtx_op_err(mtx, UMTX_OP_MUTEX_UNLOCK, 0, 0, 0);
}
Modified: stable/8/lib/libthr/thread/thr_umtx.h
==============================================================================
--- stable/8/lib/libthr/thread/thr_umtx.h Thu May 3 01:41:12 2012 (r234936)
+++ stable/8/lib/libthr/thread/thr_umtx.h Thu May 3 03:05:18 2012 (r234937)
@@ -34,6 +34,7 @@
#define DEFAULT_UMUTEX {0,0, {0,0},{0,0,0,0}}
+int _umtx_op_err(void *, int op, u_long, void *, void *) __hidden;
int __thr_umutex_lock(struct umutex *mtx, uint32_t id) __hidden;
int __thr_umutex_timedlock(struct umutex *mtx, uint32_t id,
const struct timespec *timeout) __hidden;
@@ -100,9 +101,9 @@ _thr_umutex_timedlock(struct umutex *mtx
static inline int
_thr_umutex_unlock(struct umutex *mtx, uint32_t id)
{
- if (atomic_cmpset_rel_32(&mtx->m_owner, id, UMUTEX_UNOWNED))
- return (0);
- return (__thr_umutex_unlock(mtx, id));
+ if (atomic_cmpset_rel_32(&mtx->m_owner, id, UMUTEX_UNOWNED))
+ return (0);
+ return (__thr_umutex_unlock(mtx, id));
}
static inline int
Modified: stable/8/sys/kern/kern_umtx.c
==============================================================================
--- stable/8/sys/kern/kern_umtx.c Thu May 3 01:41:12 2012 (r234936)
+++ stable/8/sys/kern/kern_umtx.c Thu May 3 03:05:18 2012 (r234937)
@@ -1261,6 +1261,78 @@ do_wake_umutex(struct thread *td, struct
return (0);
}
+/*
+ * Check if the mutex has waiters and tries to fix contention bit.
+ */
+static int
+do_wake2_umutex(struct thread *td, struct umutex *m, uint32_t flags)
+{
+ struct umtx_key key;
+ uint32_t owner, old;
+ int type;
+ int error;
+ int count;
+
+ switch(flags & (UMUTEX_PRIO_INHERIT | UMUTEX_PRIO_PROTECT)) {
+ case 0:
+ type = TYPE_NORMAL_UMUTEX;
+ break;
+ case UMUTEX_PRIO_INHERIT:
+ type = TYPE_PI_UMUTEX;
+ break;
+ case UMUTEX_PRIO_PROTECT:
+ type = TYPE_PP_UMUTEX;
+ break;
+ default:
+ return (EINVAL);
+ }
+ if ((error = umtx_key_get(m, type, GET_SHARE(flags),
+ &key)) != 0)
+ return (error);
+
+ owner = 0;
+ umtxq_lock(&key);
+ umtxq_busy(&key);
+ count = umtxq_count(&key);
+ umtxq_unlock(&key);
+ /*
+ * Only repair contention bit if there is a waiter, this means the mutex
+ * is still being referenced by userland code, otherwise don't update
+ * any memory.
+ */
+ if (count > 1) {
+ owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
+ while ((owner & UMUTEX_CONTESTED) ==0) {
+ old = casuword32(&m->m_owner, owner,
+ owner|UMUTEX_CONTESTED);
+ if (old == owner)
+ break;
+ owner = old;
+ }
+ } else if (count == 1) {
+ owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
+ while ((owner & ~UMUTEX_CONTESTED) != 0 &&
+ (owner & UMUTEX_CONTESTED) == 0) {
+ old = casuword32(&m->m_owner, owner,
+ owner|UMUTEX_CONTESTED);
+ if (old == owner)
+ break;
+ owner = old;
+ }
+ }
+ umtxq_lock(&key);
+ if (owner == -1) {
+ error = EFAULT;
+ umtxq_signal(&key, INT_MAX);
+ }
+ else if (count != 0 && (owner & ~UMUTEX_CONTESTED) == 0)
+ umtxq_signal(&key, 1);
+ umtxq_unbusy(&key);
+ umtxq_unlock(&key);
+ umtx_key_release(&key);
+ return (error);
+}
+
static inline struct umtx_pi *
umtx_pi_alloc(int flags)
{
@@ -3026,6 +3098,18 @@ __umtx_op_rw_unlock(struct thread *td, s
return do_rw_unlock(td, uap->obj);
}
+static int
+__umtx_op_wake2_umutex(struct thread *td, struct _umtx_op_args *uap)
+{
+ return do_wake2_umutex(td, uap->obj, uap->val);
+}
+
+static int
+__umtx_op_not_sup(struct thread *td __unused, struct _umtx_op_args *uap __unused)
+{
+ return ENOTSUP;
+}
+
typedef int (*_umtx_op_func)(struct thread *td, struct _umtx_op_args *uap);
static _umtx_op_func op_table[] = {
@@ -3047,7 +3131,11 @@ static _umtx_op_func op_table[] = {
__umtx_op_wait_uint_private, /* UMTX_OP_WAIT_UINT_PRIVATE */
__umtx_op_wake_private, /* UMTX_OP_WAKE_PRIVATE */
__umtx_op_wait_umutex, /* UMTX_OP_UMUTEX_WAIT */
- __umtx_op_wake_umutex /* UMTX_OP_UMUTEX_WAKE */
+ __umtx_op_wake_umutex, /* UMTX_OP_UMUTEX_WAKE */
+ __umtx_op_not_sup, /* UMTX_OP_SEM_WAIT */
+ __umtx_op_not_sup, /* UMTX_OP_SEM_WAKE */
+ __umtx_op_not_sup, /* UMTX_OP_NWAKE_PRIVATE */
+ __umtx_op_wake2_umutex /* UMTX_OP_UMUTEX_WAKE2 */
};
int
@@ -3266,7 +3354,11 @@ static _umtx_op_func op_table_compat32[]
__umtx_op_wait_uint_private_compat32, /* UMTX_OP_WAIT_UINT_PRIVATE */
__umtx_op_wake_private, /* UMTX_OP_WAKE_PRIVATE */
__umtx_op_wait_umutex_compat32, /* UMTX_OP_UMUTEX_WAIT */
- __umtx_op_wake_umutex /* UMTX_OP_UMUTEX_WAKE */
+ __umtx_op_wake_umutex, /* UMTX_OP_UMUTEX_WAKE */
+ __umtx_op_not_sup, /* UMTX_OP_SEM_WAIT */
+ __umtx_op_not_sup, /* UMTX_OP_SEM_WAKE */
+ __umtx_op_not_sup, /* UMTX_OP_NWAKE_PRIVATE */
+ __umtx_op_wake2_umutex /* UMTX_OP_UMUTEX_WAKE2 */
};
int
Modified: stable/8/sys/sys/umtx.h
==============================================================================
--- stable/8/sys/sys/umtx.h Thu May 3 01:41:12 2012 (r234936)
+++ stable/8/sys/sys/umtx.h Thu May 3 03:05:18 2012 (r234937)
@@ -100,10 +100,11 @@ struct urwlock {
#define UMTX_OP_RW_WRLOCK 13
#define UMTX_OP_RW_UNLOCK 14
#define UMTX_OP_WAIT_UINT_PRIVATE 15
-#define UMTX_OP_WAKE_PRIVATE 16
-#define UMTX_OP_MUTEX_WAIT 17
-#define UMTX_OP_MUTEX_WAKE 18
-#define UMTX_OP_MAX 19
+#define UMTX_OP_WAKE_PRIVATE 16
+#define UMTX_OP_MUTEX_WAIT 17
+#define UMTX_OP_MUTEX_WAKE 18
+#define UMTX_OP_MUTEX_WAKE2 22
+#define UMTX_OP_MAX 23
/* flags for UMTX_OP_CV_WAIT */
#define UMTX_CHECK_UNPARKING 0x01
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