Date: Tue, 17 Apr 2012 09:09:14 +0000 (UTC) From: David Xu <davidxu@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org Subject: svn commit: r234372 - stable/9/lib/libthr/thread Message-ID: <201204170909.q3H99E1E074489@svn.freebsd.org>
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Author: davidxu Date: Tue Apr 17 09:09:14 2012 New Revision: 234372 URL: http://svn.freebsd.org/changeset/base/234372 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/9: And add code to detect if the UMTX_OP_MUTEX_WAKE2 is available. Modified: stable/9/lib/libthr/thread/thr_private.h stable/9/lib/libthr/thread/thr_umtx.c stable/9/lib/libthr/thread/thr_umtx.h Directory Properties: stable/9/lib/libthr/ (props changed) Modified: stable/9/lib/libthr/thread/thr_private.h ============================================================================== --- stable/9/lib/libthr/thread/thr_private.h Tue Apr 17 09:02:55 2012 (r234371) +++ stable/9/lib/libthr/thread/thr_private.h Tue Apr 17 09:09:14 2012 (r234372) @@ -832,8 +832,6 @@ 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/9/lib/libthr/thread/thr_umtx.c ============================================================================== --- stable/9/lib/libthr/thread/thr_umtx.c Tue Apr 17 09:02:55 2012 (r234371) +++ stable/9/lib/libthr/thread/thr_umtx.c Tue Apr 17 09:09:14 2012 (r234372) @@ -152,13 +152,35 @@ __thr_umutex_timedlock(struct umutex *mt int __thr_umutex_unlock(struct umutex *mtx, uint32_t id) { -#ifndef __ia64__ - /* XXX this logic has a race-condition on ia64. */ - if ((mtx->m_flags & (UMUTEX_PRIO_PROTECT | UMUTEX_PRIO_INHERIT)) == 0) { - atomic_cmpset_rel_32(&mtx->m_owner, id | UMUTEX_CONTESTED, UMUTEX_CONTESTED); - return _umtx_op_err(mtx, UMTX_OP_MUTEX_WAKE, 0, 0, 0); + 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); } -#endif /* __ia64__ */ +unlock: return _umtx_op_err(mtx, UMTX_OP_MUTEX_UNLOCK, 0, 0, 0); } Modified: stable/9/lib/libthr/thread/thr_umtx.h ============================================================================== --- stable/9/lib/libthr/thread/thr_umtx.h Tue Apr 17 09:02:55 2012 (r234371) +++ stable/9/lib/libthr/thread/thr_umtx.h Tue Apr 17 09:09:14 2012 (r234372) @@ -35,6 +35,7 @@ #define DEFAULT_UMUTEX {0,0,{0,0},{0,0,0,0}} #define DEFAULT_URWLOCK {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_lock_spin(struct umutex *mtx, uint32_t id) __hidden; int __thr_umutex_timedlock(struct umutex *mtx, uint32_t id, @@ -119,9 +120,9 @@ _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
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