Author: mjg
Date: Wed Jun 1 18:32:20 2016
New Revision: 301157
URL: https://svnweb.freebsd.org/changeset/base/301157
Log:
Microoptimize locking primitives by avoiding unnecessary atomic ops.
Inline version of primitives do an atomic op and if it fails they fallback to
actual primitives, which immediately retry the atomic op.
The obvious optimisation is to check if the lock is free and only then proceed
to do an atomic op.
Reviewed by: jhb, vangyzen
Modified:
head/sys/kern/kern_lock.c
head/sys/kern/kern_mutex.c
head/sys/kern/kern_rwlock.c
head/sys/kern/kern_sx.c
head/sys/sys/mutex.h
head/sys/sys/rwlock.h
head/sys/sys/sx.h
Modified: head/sys/kern/kern_lock.c
==============================================================================
--- head/sys/kern/kern_lock.c Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/kern/kern_lock.c Wed Jun 1 18:32:20 2016 (r301157)
@@ -787,8 +787,10 @@ __lockmgr_args(struct lock *lk, u_int fl
break;
}
- while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED,
- tid)) {
+ for (;;) {
+ if (lk->lk_lock == LK_UNLOCKED &&
+ atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED,
tid))
+ break;
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
@@ -1124,7 +1126,11 @@ __lockmgr_args(struct lock *lk, u_int fl
__func__, iwmesg, file, line);
}
- while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
+ for (;;) {
+ if (lk->lk_lock == LK_UNLOCKED &&
+ atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED,
tid))
+ break;
+
#ifdef HWPMC_HOOKS
PMC_SOFT_CALL( , , lock, failed);
#endif
Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/kern/kern_mutex.c Wed Jun 1 18:32:20 2016 (r301157)
@@ -419,7 +419,9 @@ __mtx_lock_sleep(volatile uintptr_t *c,
all_time -= lockstat_nsecs(&m->lock_object);
#endif
- while (!_mtx_obtain_lock(m, tid)) {
+ for (;;) {
+ if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m, tid))
+ break;
#ifdef KDTRACE_HOOKS
spin_cnt++;
#endif
@@ -602,8 +604,9 @@ _mtx_lock_spin_cookie(volatile uintptr_t
#ifdef KDTRACE_HOOKS
spin_time -= lockstat_nsecs(&m->lock_object);
#endif
- while (!_mtx_obtain_lock(m, tid)) {
-
+ for (;;) {
+ if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m, tid))
+ break;
/* Give interrupts a chance while we spin. */
spinlock_exit();
while (m->mtx_lock != MTX_UNOWNED) {
@@ -675,7 +678,9 @@ retry:
m->lock_object.lo_name, file, line));
WITNESS_CHECKORDER(&m->lock_object,
opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
- while (!_mtx_obtain_lock(m, tid)) {
+ for (;;) {
+ if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m,
tid))
+ break;
if (m->mtx_lock == tid) {
m->mtx_recurse++;
break;
Modified: head/sys/kern/kern_rwlock.c
==============================================================================
--- head/sys/kern/kern_rwlock.c Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/kern/kern_rwlock.c Wed Jun 1 18:32:20 2016 (r301157)
@@ -771,7 +771,9 @@ __rw_wlock_hard(volatile uintptr_t *c, u
all_time -= lockstat_nsecs(&rw->lock_object);
state = rw->rw_lock;
#endif
- while (!_rw_write_lock(rw, tid)) {
+ for (;;) {
+ if (rw->rw_lock == RW_UNLOCKED && _rw_write_lock(rw, tid))
+ break;
#ifdef KDTRACE_HOOKS
spin_cnt++;
#endif
Modified: head/sys/kern/kern_sx.c
==============================================================================
--- head/sys/kern/kern_sx.c Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/kern/kern_sx.c Wed Jun 1 18:32:20 2016 (r301157)
@@ -544,7 +544,10 @@ _sx_xlock_hard(struct sx *sx, uintptr_t
all_time -= lockstat_nsecs(&sx->lock_object);
state = sx->sx_lock;
#endif
- while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
+ for (;;) {
+ if (sx->sx_lock == SX_LOCK_UNLOCKED &&
+ atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
+ break;
#ifdef KDTRACE_HOOKS
spin_cnt++;
#endif
Modified: head/sys/sys/mutex.h
==============================================================================
--- head/sys/sys/mutex.h Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/sys/mutex.h Wed Jun 1 18:32:20 2016 (r301157)
@@ -185,7 +185,7 @@ void thread_lock_flags_(struct thread *,
#define __mtx_lock(mp, tid, opts, file, line) do { \
uintptr_t _tid = (uintptr_t)(tid); \
\
- if (!_mtx_obtain_lock((mp), _tid)) \
+ if (((mp)->mtx_lock != MTX_UNOWNED || !_mtx_obtain_lock((mp), _tid)))\
_mtx_lock_sleep((mp), _tid, (opts), (file), (line)); \
else \
LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(adaptive__acquire, \
@@ -203,7 +203,7 @@ void thread_lock_flags_(struct thread *,
uintptr_t _tid = (uintptr_t)(tid); \
\
spinlock_enter(); \
- if (!_mtx_obtain_lock((mp), _tid)) { \
+ if (((mp)->mtx_lock != MTX_UNOWNED || !_mtx_obtain_lock((mp), _tid))) {\
if ((mp)->mtx_lock == _tid) \
(mp)->mtx_recurse++; \
else \
@@ -232,7 +232,7 @@ void thread_lock_flags_(struct thread *,
\
if ((mp)->mtx_recurse == 0) \
LOCKSTAT_PROFILE_RELEASE_LOCK(adaptive__release, mp); \
- if (!_mtx_release_lock((mp), _tid)) \
+ if ((mp)->mtx_lock != _tid || !_mtx_release_lock((mp), _tid)) \
_mtx_unlock_sleep((mp), (opts), (file), (line)); \
} while (0)
Modified: head/sys/sys/rwlock.h
==============================================================================
--- head/sys/sys/rwlock.h Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/sys/rwlock.h Wed Jun 1 18:32:20 2016 (r301157)
@@ -96,7 +96,7 @@
#define __rw_wlock(rw, tid, file, line) do {
\
uintptr_t _tid = (uintptr_t)(tid); \
\
- if (!_rw_write_lock((rw), _tid)) \
+ if ((rw)->rw_lock != RW_UNLOCKED || !_rw_write_lock((rw), _tid))\
_rw_wlock_hard((rw), _tid, (file), (line)); \
else \
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, \
@@ -112,7 +112,7 @@
else { \
LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, \
LOCKSTAT_WRITER); \
- if (!_rw_write_unlock((rw), _tid)) \
+ if ((rw)->rw_lock != _tid || !_rw_write_unlock((rw), _tid))\
_rw_wunlock_hard((rw), _tid, (file), (line)); \
} \
} while (0)
Modified: head/sys/sys/sx.h
==============================================================================
--- head/sys/sys/sx.h Wed Jun 1 17:57:56 2016 (r301156)
+++ head/sys/sys/sx.h Wed Jun 1 18:32:20 2016 (r301157)
@@ -150,7 +150,8 @@ __sx_xlock(struct sx *sx, struct thread
uintptr_t tid = (uintptr_t)td;
int error = 0;
- if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
+ if (sx->sx_lock != SX_LOCK_UNLOCKED ||
+ !atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
error = _sx_xlock_hard(sx, tid, opts, file, line);
else
LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
@@ -168,7 +169,8 @@ __sx_xunlock(struct sx *sx, struct threa
if (sx->sx_recurse == 0)
LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx,
LOCKSTAT_WRITER);
- if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
+ if (sx->sx_lock != tid ||
+ !atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
_sx_xunlock_hard(sx, tid, file, line);
}
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