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Commit64b1fb5

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Optimize pg_atomic_exchange_u32 and pg_atomic_exchange_u64.
Presently, all platforms implement atomic exchanges by performingan atomic compare-and-swap in a loop until it succeeds. This canbe especially expensive when there is contention on the atomicvariable. This commit optimizes atomic exchanges on many platformsby using compiler intrinsics, which should compile into somethingmuch less expensive than a compare-and-swap loop. Since theseintrinsics have been available for some time, the inline assemblyimplementations are omitted.Suggested-by: Andres FreundReviewed-by: Andres FreundDiscussion:https://postgr.es/m/20231129212905.GA1258737%40nathanxps13
1 parent0d1adae commit64b1fb5

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3 files changed

+66
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3 files changed

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‎src/include/port/atomics/generic-gcc.h

Lines changed: 34 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -176,6 +176,23 @@ pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
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}
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#endif
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/*
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* __sync_lock_test_and_set() only supports setting the value to 1 on some
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* platforms, so we only provide an __atomic implementation for
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* pg_atomic_exchange.
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*
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* We assume the availability of 32-bit __atomic_compare_exchange_n() implies
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* the availability of 32-bit __atomic_exchange_n().
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*/
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#if !defined(PG_HAVE_ATOMIC_EXCHANGE_U32)&& defined(HAVE_GCC__ATOMIC_INT32_CAS)
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#definePG_HAVE_ATOMIC_EXCHANGE_U32
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staticinlineuint32
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pg_atomic_exchange_u32_impl(volatilepg_atomic_uint32*ptr,uint32newval)
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{
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return__atomic_exchange_n(&ptr->value,newval,__ATOMIC_SEQ_CST);
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}
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#endif
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/* if we have 32-bit __sync_val_compare_and_swap, assume we have these too: */
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181198
#if !defined(PG_HAVE_ATOMIC_FETCH_ADD_U32)&& defined(HAVE_GCC__SYNC_INT32_CAS)
@@ -243,6 +260,23 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
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}
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#endif
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/*
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* __sync_lock_test_and_set() only supports setting the value to 1 on some
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* platforms, so we only provide an __atomic implementation for
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* pg_atomic_exchange.
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*
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* We assume the availability of 64-bit __atomic_compare_exchange_n() implies
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* the availability of 64-bit __atomic_exchange_n().
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*/
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#if !defined(PG_HAVE_ATOMIC_EXCHANGE_U64)&& defined(HAVE_GCC__ATOMIC_INT64_CAS)
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#definePG_HAVE_ATOMIC_EXCHANGE_U64
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staticinlineuint64
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pg_atomic_exchange_u64_impl(volatilepg_atomic_uint64*ptr,uint64newval)
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{
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return__atomic_exchange_n(&ptr->value,newval,__ATOMIC_SEQ_CST);
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}
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#endif
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/* if we have 64-bit __sync_val_compare_and_swap, assume we have these too: */
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#if !defined(PG_HAVE_ATOMIC_FETCH_ADD_U64)&& defined(HAVE_GCC__SYNC_INT64_CAS)

‎src/include/port/atomics/generic-msvc.h

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -58,6 +58,13 @@ pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
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returnret;
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}
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#definePG_HAVE_ATOMIC_EXCHANGE_U32
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staticinlineuint32
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pg_atomic_exchange_u32_impl(volatilepg_atomic_uint32*ptr,uint32newval)
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{
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returnInterlockedExchange(&ptr->value,newval);
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}
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#definePG_HAVE_ATOMIC_FETCH_ADD_U32
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staticinlineuint32
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pg_atomic_fetch_add_u32_impl(volatilepg_atomic_uint32*ptr,int32add_)
@@ -88,6 +95,16 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
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/* Only implemented on 64bit builds */
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#ifdef_WIN64
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#pragma intrinsic(_InterlockedExchange64)
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#definePG_HAVE_ATOMIC_EXCHANGE_U64
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staticinlineuint64
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pg_atomic_exchange_u64_impl(volatilepg_atomic_uint64*ptr,uint64newval)
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{
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return_InterlockedExchange64(&ptr->value,newval);
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}
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#pragma intrinsic(_InterlockedExchangeAdd64)
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#definePG_HAVE_ATOMIC_FETCH_ADD_U64
@@ -96,6 +113,7 @@ pg_atomic_fetch_add_u64_impl(volatile pg_atomic_uint64 *ptr, int64 add_)
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{
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return_InterlockedExchangeAdd64(&ptr->value,add_);
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}
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#endif/* _WIN64 */
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#endif/* HAVE_ATOMICS */

‎src/include/port/atomics/generic-sunpro.h

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -87,6 +87,13 @@ pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
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returnret;
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}
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#definePG_HAVE_ATOMIC_EXCHANGE_U32
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staticinlineuint32
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pg_atomic_exchange_u32_impl(volatilepg_atomic_uint32*ptr,uint32newval)
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{
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returnatomic_swap_32(&ptr->value,newval);
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}
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#definePG_HAVE_ATOMIC_COMPARE_EXCHANGE_U64
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staticinlinebool
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pg_atomic_compare_exchange_u64_impl(volatilepg_atomic_uint64*ptr,
@@ -101,6 +108,13 @@ pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
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returnret;
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}
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#definePG_HAVE_ATOMIC_EXCHANGE_U64
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staticinlineuint64
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pg_atomic_exchange_u64_impl(volatilepg_atomic_uint64*ptr,uint64newval)
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{
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returnatomic_swap_64(&ptr->value,newval);
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}
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#endif/* HAVE_ATOMIC_H */
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#endif/* defined(HAVE_ATOMICS) */

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