>From a7a2548c17c3881068053fc9bf040c9cc0c2b533 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Tue, 13 Jan 2015 11:58:04 +0100 Subject: [PATCH 09/10] WIP: lwlock.c: use latches --- src/backend/storage/lmgr/lwlock.c | 89 ++++++++++++++++++++++++++++++++------- 1 file changed, 73 insertions(+), 16 deletions(-) diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index 7ca8dc0..c159cce 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -107,6 +107,8 @@ extern slock_t *ShmemLock; /* Must be greater than MAX_BACKENDS - which is 2^23-1, so we're fine. */ #define LW_SHARED_MASK ((uint32)(1 << 23)) +#define LW_USE_LATCHES + /* * This is indexed by tranche ID and stores metadata for all tranches known * to the current backend. @@ -731,7 +733,11 @@ LWLockWakeup(LWLock *lock) */ pg_write_barrier(); waiter->lwWaiting = false; +#ifdef LW_USE_LATCHES + SetLatch(&waiter->procLatch); +#else PGSemaphoreUnlock(&waiter->sem); +#endif } } @@ -843,7 +849,9 @@ LWLockDequeueSelf(LWLock *lock) MyProc->lwWaiting = false; else { +#ifndef LW_USE_LATCHES int extraWaits = 0; +#endif /* * Somebody else dequeued us and has or will wake us up. Deal with the @@ -863,17 +871,26 @@ LWLockDequeueSelf(LWLock *lock) */ for (;;) { +#ifdef LW_USE_LATCHES + if (!MyProc->lwWaiting) + break; + WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0); + ResetLatch(&MyProc->procLatch); +#else PGSemaphoreLock(&MyProc->sem); if (!MyProc->lwWaiting) break; extraWaits++; +#endif } +#ifndef LW_USE_LATCHES /* * Fix the process wait semaphore's count for any absorbed wakeups. */ while (extraWaits-- > 0) PGSemaphoreUnlock(&MyProc->sem); +#endif } #ifdef LOCK_DEBUG @@ -914,9 +931,10 @@ LWLockAcquireWithVar(LWLock *l, uint64 *valptr, uint64 val) static inline bool LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val) { - PGPROC *proc = MyProc; bool result = true; - int extraWaits = 0; +#ifndef LW_USE_LATCHES + int extraWaits = 0; +#endif #ifdef LWLOCK_STATS lwlock_stats *lwstats; @@ -940,7 +958,7 @@ LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val) * during bootstrap or shared memory initialization. Put an Assert here * to catch unsafe coding practices. */ - Assert(!(proc == NULL && IsUnderPostmaster)); + Assert(!(MyProc == NULL && IsUnderPostmaster)); /* Ensure we will have room to remember the lock */ if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS) @@ -1033,10 +1051,19 @@ LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val) for (;;) { - PGSemaphoreLock(&proc->sem); - if (!proc->lwWaiting) +#ifdef LW_USE_LATCHES + pg_read_barrier(); + if (!MyProc->lwWaiting) + break; + + WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0); + ResetLatch(&MyProc->procLatch); +#else + PGSemaphoreLock(&MyProc->sem); + if (!MyProc->lwWaiting) break; extraWaits++; +#endif } /* Retrying, allow LWLockRelease to release waiters again. */ @@ -1068,11 +1095,13 @@ LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val) held_lwlocks[num_held_lwlocks].lock = lock; held_lwlocks[num_held_lwlocks++].mode = mode; +#ifndef LW_USE_LATCHES /* * Fix the process wait semaphore's count for any absorbed wakeups. */ while (extraWaits-- > 0) - PGSemaphoreUnlock(&proc->sem); + PGSemaphoreUnlock(&MyProc->sem); +#endif return result; } @@ -1142,9 +1171,10 @@ LWLockConditionalAcquire(LWLock *lock, LWLockMode mode) bool LWLockAcquireOrWait(LWLock *lock, LWLockMode mode) { - PGPROC *proc = MyProc; bool mustwait; - int extraWaits = 0; +#ifndef LW_USE_LATCHES + int extraWaits = 0; +#endif #ifdef LWLOCK_STATS lwlock_stats *lwstats; @@ -1193,10 +1223,19 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode) for (;;) { - PGSemaphoreLock(&proc->sem); - if (!proc->lwWaiting) +#ifdef LW_USE_LATCHES + pg_read_barrier(); + if (!MyProc->lwWaiting) + break; + + WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0); + ResetLatch(&MyProc->procLatch); +#else + PGSemaphoreLock(&MyProc->sem); + if (!MyProc->lwWaiting) break; extraWaits++; +#endif } #ifdef LOCK_DEBUG @@ -1224,11 +1263,13 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode) } } +#ifndef LW_USE_LATCHES /* * Fix the process wait semaphore's count for any absorbed wakeups. */ while (extraWaits-- > 0) - PGSemaphoreUnlock(&proc->sem); + PGSemaphoreUnlock(&MyProc->sem); +#endif if (mustwait) { @@ -1271,9 +1312,10 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode) bool LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval) { - PGPROC *proc = MyProc; - int extraWaits = 0; bool result = false; +#ifndef LW_USE_LATCHES + int extraWaits = 0; +#endif #ifdef LWLOCK_STATS lwlock_stats *lwstats; @@ -1394,10 +1436,19 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval) for (;;) { - PGSemaphoreLock(&proc->sem); - if (!proc->lwWaiting) +#ifdef LW_USE_LATCHES + pg_read_barrier(); + if (!MyProc->lwWaiting) + break; + + WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0); + ResetLatch(&MyProc->procLatch); +#else + PGSemaphoreLock(&MyProc->sem); + if (!MyProc->lwWaiting) break; extraWaits++; +#endif } #ifdef LOCK_DEBUG @@ -1418,11 +1469,13 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval) TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), T_ID(lock), LW_EXCLUSIVE); +#ifndef LW_USE_LATCHES /* * Fix the process wait semaphore's count for any absorbed wakeups. */ while (extraWaits-- > 0) - PGSemaphoreUnlock(&proc->sem); + PGSemaphoreUnlock(&MyProc->sem); +#endif /* * Now okay to allow cancel/die interrupts. @@ -1498,7 +1551,11 @@ LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 val) /* check comment in LWLockWakeup() about this barrier */ pg_write_barrier(); waiter->lwWaiting = false; +#ifdef LW_USE_LATCHES + SetLatch(&waiter->procLatch); +#else PGSemaphoreUnlock(&waiter->sem); +#endif } } -- 2.0.0.rc2.4.g1dc51c6.dirty