Hello there, quite some time ago I posted a trivial patch to locking primitives. What they do is the inline part tries an atomic op and if that fails the actual function is called, which immediately tries the same op.
The obvious optimisation checks for the availability of the lock first. There concerns about the way it was done previously by relying on volatile behaving in a specific way. Later a simplified version was posted which should not have the concern, but the thread died. I refer you to https://lists.freebsd.org/pipermail/freebsd-current/2015-November/058100.html for simple benchmark results. I would like to get the patch in before 11 freeze. diff --git a/sys/kern/kern_lock.c b/sys/kern/kern_lock.c index 34d7b34..1b10623 100644 --- a/sys/kern/kern_lock.c +++ b/sys/kern/kern_lock.c @@ -787,8 +787,10 @@ __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk, 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 flags, struct lock_object *ilk, __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 diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c index 3f62d17..d167205 100644 --- a/sys/kern/kern_mutex.c +++ b/sys/kern/kern_mutex.c @@ -419,7 +419,9 @@ __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t tid, int opts, 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 *c, uintptr_t tid, int opts, #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; diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c index 6541724..6a904d2 100644 --- a/sys/kern/kern_rwlock.c +++ b/sys/kern/kern_rwlock.c @@ -771,7 +771,9 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file, 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 diff --git a/sys/kern/kern_sx.c b/sys/kern/kern_sx.c index 96e117b..2a81c04 100644 --- a/sys/kern/kern_sx.c +++ b/sys/kern/kern_sx.c @@ -544,7 +544,10 @@ _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 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 diff --git a/sys/sys/mutex.h b/sys/sys/mutex.h index a9ec072..0443922 100644 --- a/sys/sys/mutex.h +++ b/sys/sys/mutex.h @@ -185,7 +185,7 @@ void thread_lock_flags_(struct thread *, int, const char *, int); #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 *, int, const char *, int); 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 *, int, const char *, int); \ 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) diff --git a/sys/sys/rwlock.h b/sys/sys/rwlock.h index f8947c5..6b4f505 100644 --- a/sys/sys/rwlock.h +++ b/sys/sys/rwlock.h @@ -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) diff --git a/sys/sys/sx.h b/sys/sys/sx.h index 03b51d3..57a31d9 100644 --- a/sys/sys/sx.h +++ b/sys/sys/sx.h @@ -150,7 +150,8 @@ __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file, 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 thread *td, const char *file, int line) 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); } _______________________________________________ freebsd-current@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
