Remove --disable-spinlocks.

A later change will require atomic support, so it wouldn't make sense
for a hypothetical new system not to be able to implement spinlocks.

Reviewed-by: Heikki Linnakangas <[email protected]>
Reviewed-by: Tom Lane <[email protected]> (concept, not the patch)
Reviewed-by: Andres Freund <[email protected]> (concept, not the patch)
Discussion: https://postgr.es/m/3351991.1697728588%40sss.pgh.pa.us

Author: macdice

configure

@@ -836,7 +836,6 @@ enable_integer_datetimes
 enable_nls
 with_pgport
 enable_rpath
-enable_spinlocks
 enable_atomics
 enable_debug
 enable_profiling
@@ -1529,7 +1528,6 @@ Optional Features:
                           enable Native Language Support
   --disable-rpath         do not embed shared library search path in
                           executables
-  --disable-spinlocks     do not use spinlocks
   --disable-atomics       do not use atomic operations
   --enable-debug          build with debugging symbols (-g)
   --enable-profiling      build with profiling enabled
@@ -3266,33 +3264,6 @@ fi
 
 
 
-#
-# Spinlocks
-#
-
-
-# Check whether --enable-spinlocks was given.
-if test "${enable_spinlocks+set}" = set; then :
-  enableval=$enable_spinlocks;
-  case $enableval in
-    yes)
-      :
-      ;;
-    no)
-      :
-      ;;
-    *)
-      as_fn_error $? "no argument expected for --enable-spinlocks option" "$LINENO" 5
-      ;;
-  esac
-
-else
-  enable_spinlocks=yes
-
-fi
-
-
-
 #
 # Atomic operations
 #
@@ -12185,17 +12156,6 @@ fi
 
 fi
 
-if test "$enable_spinlocks" = yes; then
-
-$as_echo "#define HAVE_SPINLOCKS 1" >>confdefs.h
-
-else
-  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING:
-*** Not using spinlocks will cause poor performance." >&5
-$as_echo "$as_me: WARNING:
-*** Not using spinlocks will cause poor performance." >&2;}
-fi
-
 if test "$enable_atomics" = yes; then
 
 $as_echo "#define HAVE_ATOMICS 1" >>confdefs.h

configure.ac

@@ -186,12 +186,6 @@ PGAC_ARG_BOOL(enable, rpath, yes,
               [do not embed shared library search path in executables])
 AC_SUBST(enable_rpath)
 
-#
-# Spinlocks
-#
-PGAC_ARG_BOOL(enable, spinlocks, yes,
-              [do not use spinlocks])
-
 #
 # Atomic operations
 #
@@ -1296,13 +1290,6 @@ failure.  It is possible the compiler isn't looking in the proper directory.
 Use --without-zlib to disable zlib support.])])
 fi
 
-if test "$enable_spinlocks" = yes; then
-  AC_DEFINE(HAVE_SPINLOCKS, 1, [Define to 1 if you have spinlocks.])
-else
-  AC_MSG_WARN([
-*** Not using spinlocks will cause poor performance.])
-fi
-
 if test "$enable_atomics" = yes; then
   AC_DEFINE(HAVE_ATOMICS, 1, [Define to 1 if you want to use atomics if available.])
 else

doc/src/sgml/installation.sgml

@@ -1258,22 +1258,6 @@ build-postgresql:
        </listitem>
       </varlistentry>
 
-      <varlistentry id="configure-option-disable-spinlocks">
-       <term><option>--disable-spinlocks</option></term>
-       <listitem>
-        <para>
-         Allow the build to succeed even if <productname>PostgreSQL</productname>
-         has no CPU spinlock support for the platform.  The lack of
-         spinlock support will result in very poor performance; therefore,
-         this option should only be used if the build aborts and
-         informs you that the platform lacks spinlock support. If this
-         option is required to build <productname>PostgreSQL</productname> on
-         your platform, please report the problem to the
-         <productname>PostgreSQL</productname> developers.
-        </para>
-       </listitem>
-      </varlistentry>
-
       <varlistentry id="configure-option-disable-atomics">
        <term><option>--disable-atomics</option></term>
        <listitem>
@@ -2690,23 +2674,6 @@ ninja install
       </listitem>
      </varlistentry>
 
-     <varlistentry id="configure-spinlocks-meson">
-      <term><option>-Dspinlocks={ true | false }</option></term>
-      <listitem>
-       <para>
-        This option is set to true by default; setting it to false will
-        allow the build to succeed even if <productname>PostgreSQL</productname>
-        has no CPU spinlock support for the platform.  The lack of
-        spinlock support will result in very poor performance; therefore,
-        this option should only be changed if the build aborts and
-        informs you that the platform lacks spinlock support. If setting this
-        option to false is required to build <productname>PostgreSQL</productname> on
-        your platform, please report the problem to the
-        <productname>PostgreSQL</productname> developers.
-       </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="configure-atomics-meson">
       <term><option>-Datomics={ true | false }</option></term>
       <listitem>
@@ -2719,6 +2686,7 @@ ninja install
        </para>
       </listitem>
      </varlistentry>
+
     </variablelist>
    </sect3>
 
@@ -3393,9 +3361,6 @@ export MANPATH
    these CPU architectures: x86, PowerPC, S/390, SPARC, ARM, MIPS,
    and RISC-V, including
    big-endian, little-endian, 32-bit, and 64-bit variants where applicable.
-   It is often
-   possible to build on an unsupported CPU type by configuring with
-   <option>--disable-spinlocks</option>, but performance will be poor.
   </para>
 
   <para>

meson.build

@@ -2089,12 +2089,6 @@ endif
 # Atomics
 ###############################################################
 
-if not get_option('spinlocks')
-  warning('Not using spinlocks will cause poor performance')
-else
-  cdata.set('HAVE_SPINLOCKS', 1)
-endif
-
 if not get_option('atomics')
   warning('Not using atomics will cause poor performance')
 else

src/backend/port/atomics.c

@@ -57,17 +57,7 @@ pg_atomic_init_flag_impl(volatile pg_atomic_flag *ptr)
 	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_flag vs slock_t");
 
-#ifndef HAVE_SPINLOCKS
-
-	/*
-	 * NB: If we're using semaphore based TAS emulation, be careful to use a
-	 * separate set of semaphores. Otherwise we'd get in trouble if an atomic
-	 * var would be manipulated while spinlock is held.
-	 */
-	s_init_lock_sema((slock_t *) &ptr->sema, true);
-#else
 	SpinLockInit((slock_t *) &ptr->sema);
-#endif
 
 	ptr->value = false;
 }
@@ -108,15 +98,7 @@ pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_)
 	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_uint32 vs slock_t");
 
-	/*
-	 * If we're using semaphore based atomic flags, be careful about nested
-	 * usage of atomics while a spinlock is held.
-	 */
-#ifndef HAVE_SPINLOCKS
-	s_init_lock_sema((slock_t *) &ptr->sema, true);
-#else
 	SpinLockInit((slock_t *) &ptr->sema);
-#endif
 	ptr->value = val_;
 }
 
@@ -184,15 +166,7 @@ pg_atomic_init_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val_)
 	StaticAssertDecl(sizeof(ptr->sema) >= sizeof(slock_t),
 					 "size mismatch of atomic_uint64 vs slock_t");
 
-	/*
-	 * If we're using semaphore based atomic flags, be careful about nested
-	 * usage of atomics while a spinlock is held.
-	 */
-#ifndef HAVE_SPINLOCKS
-	s_init_lock_sema((slock_t *) &ptr->sema, true);
-#else
 	SpinLockInit((slock_t *) &ptr->sema);
-#endif
 	ptr->value = val_;
 }
 

src/backend/port/posix_sema.c

@@ -217,8 +217,7 @@ PGReserveSemaphores(int maxSemas)
 
 	/*
 	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
-	 * ShmemAlloc() won't be ready yet.  (This ordering is necessary when we
-	 * are emulating spinlocks with semaphores.)
+	 * ShmemAlloc() won't be ready yet.
 	 */
 	sharedSemas = (PGSemaphore)
 		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));

src/backend/port/sysv_sema.c

@@ -325,8 +325,7 @@ PGReserveSemaphores(int maxSemas)
 
 	/*
 	 * We must use ShmemAllocUnlocked(), since the spinlock protecting
-	 * ShmemAlloc() won't be ready yet.  (This ordering is necessary when we
-	 * are emulating spinlocks with semaphores.)
+	 * ShmemAlloc() won't be ready yet.
 	 */
 	sharedSemas = (PGSemaphore)
 		ShmemAllocUnlocked(PGSemaphoreShmemSize(maxSemas));

src/backend/postmaster/launch_backend.c

@@ -108,9 +108,7 @@ typedef struct
 #ifdef USE_INJECTION_POINTS
 	struct InjectionPointsCtl *ActiveInjectionPoints;
 #endif
-#ifndef HAVE_SPINLOCKS
 	PGSemaphore *SpinlockSemaArray;
-#endif
 	int			NamedLWLockTrancheRequests;
 	NamedLWLockTranche *NamedLWLockTrancheArray;
 	LWLockPadded *MainLWLockArray;
@@ -724,9 +722,6 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
 	param->ActiveInjectionPoints = ActiveInjectionPoints;
 #endif
 
-#ifndef HAVE_SPINLOCKS
-	param->SpinlockSemaArray = SpinlockSemaArray;
-#endif
 	param->NamedLWLockTrancheRequests = NamedLWLockTrancheRequests;
 	param->NamedLWLockTrancheArray = NamedLWLockTrancheArray;
 	param->MainLWLockArray = MainLWLockArray;
@@ -986,9 +981,6 @@ restore_backend_variables(BackendParameters *param)
 	ActiveInjectionPoints = param->ActiveInjectionPoints;
 #endif
 
-#ifndef HAVE_SPINLOCKS
-	SpinlockSemaArray = param->SpinlockSemaArray;
-#endif
 	NamedLWLockTrancheRequests = param->NamedLWLockTrancheRequests;
 	NamedLWLockTrancheArray = param->NamedLWLockTrancheArray;
 	MainLWLockArray = param->MainLWLockArray;

src/backend/storage/ipc/ipci.c

@@ -94,7 +94,6 @@ CalculateShmemSize(int *num_semaphores)
 
 	/* Compute number of semaphores we'll need */
 	numSemas = ProcGlobalSemas();
-	numSemas += SpinlockSemas();
 
 	/* Return the number of semaphores if requested by the caller */
 	if (num_semaphores)
@@ -111,7 +110,6 @@ CalculateShmemSize(int *num_semaphores)
 	 */
 	size = 100000;
 	size = add_size(size, PGSemaphoreShmemSize(numSemas));
-	size = add_size(size, SpinlockSemaSize());
 	size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
 											 sizeof(ShmemIndexEnt)));
 	size = add_size(size, dsm_estimate_size());
@@ -225,14 +223,6 @@ CreateSharedMemoryAndSemaphores(void)
 	 */
 	PGReserveSemaphores(numSemas);
 
-	/*
-	 * If spinlocks are disabled, initialize emulation layer (which depends on
-	 * semaphores, so the order is important here).
-	 */
-#ifndef HAVE_SPINLOCKS
-	SpinlockSemaInit();
-#endif
-
 	/*
 	 * Set up shared memory allocation mechanism
 	 */

src/backend/storage/lmgr/Makefile

@@ -21,7 +21,6 @@ OBJS = \
 	predicate.o \
 	proc.o \
 	s_lock.o \
-	spin.o
 
 include $(top_srcdir)/src/backend/common.mk
 

src/backend/storage/lmgr/meson.build

@@ -9,5 +9,4 @@ backend_sources += files(
   'predicate.c',
   'proc.c',
   's_lock.c',
-  'spin.c',
 )

src/backend/storage/lmgr/s_lock.c

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * s_lock.c
- *	   Hardware-dependent implementation of spinlocks.
+ *	   Implementation of spinlocks.
  *
  * When waiting for a contended spinlock we loop tightly for awhile, then
  * delay using pg_usleep() and try again.  Preferably, "awhile" should be a