I wrote:
> So at this point I'm not sure what to do. I could back out the back-patch
> of 44cd47c1d49655c5, which would mean accepting that 9.2/9.3 are broken
> and will never be fixed for HPPA, as well as any other architectures that
> use the same fallback memory barrier implementation. The lack of
> complaints from the field suggests that nobody would care. Or I could
> push forward by back-patching daa7527afc227443 (and a couple of minor
> follow-on cleanups). That doesn't seem particularly risky, now that
> 9.4's been out for awhile, but it's kind of a large back-patch to benefit
> architectures that apparently no actual users care about.
I went ahead and prepared and tested such a patch; the version for 9.3
is attached. (9.2 is identical modulo some pgindent-induced whitespace
difference.) This doesn't look too hazardous to me, so I'm thinking
we should apply it.
regards, tom lane
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 3808836..fc4abbc 100644
*** a/src/backend/postmaster/postmaster.c
--- b/src/backend/postmaster/postmaster.c
*************** typedef struct
*** 500,505 ****
--- 500,508 ----
slock_t *ShmemLock;
VariableCache ShmemVariableCache;
Backend *ShmemBackendArray;
+ #ifndef HAVE_SPINLOCKS
+ PGSemaphore SpinlockSemaArray;
+ #endif
LWLock *LWLockArray;
slock_t *ProcStructLock;
PROC_HDR *ProcGlobal;
*************** save_backend_variables(BackendParameters
*** 6050,6055 ****
--- 6053,6061 ----
param->ShmemVariableCache = ShmemVariableCache;
param->ShmemBackendArray = ShmemBackendArray;
+ #ifndef HAVE_SPINLOCKS
+ param->SpinlockSemaArray = SpinlockSemaArray;
+ #endif
param->LWLockArray = LWLockArray;
param->ProcStructLock = ProcStructLock;
param->ProcGlobal = ProcGlobal;
*************** restore_backend_variables(BackendParamet
*** 6278,6283 ****
--- 6284,6292 ----
ShmemVariableCache = param->ShmemVariableCache;
ShmemBackendArray = param->ShmemBackendArray;
+ #ifndef HAVE_SPINLOCKS
+ SpinlockSemaArray = param->SpinlockSemaArray;
+ #endif
LWLockArray = param->LWLockArray;
ProcStructLock = param->ProcStructLock;
ProcGlobal = param->ProcGlobal;
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 918ac51..ec8e4f6 100644
*** a/src/backend/storage/ipc/ipci.c
--- b/src/backend/storage/ipc/ipci.c
*************** CreateSharedMemoryAndSemaphores(bool mak
*** 103,108 ****
--- 103,109 ----
* need to be so careful during the actual allocation phase.
*/
size = 100000;
+ size = add_size(size, SpinlockSemaSize());
size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
sizeof(ShmemIndexEnt)));
size = add_size(size, BufferShmemSize());
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 129d9f8..4194db6 100644
*** a/src/backend/storage/ipc/shmem.c
--- b/src/backend/storage/ipc/shmem.c
*************** InitShmemAllocation(void)
*** 116,124 ****
Assert(shmhdr != NULL);
/*
! * Initialize the spinlock used by ShmemAlloc. We have to do the space
! * allocation the hard way, since obviously ShmemAlloc can't be called
! * yet.
*/
ShmemLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset);
shmhdr->freeoffset += MAXALIGN(sizeof(slock_t));
--- 116,139 ----
Assert(shmhdr != NULL);
/*
! * If spinlocks are disabled, initialize emulation layer. We have to do
! * the space allocation the hard way, since obviously ShmemAlloc can't be
! * called yet.
! */
! #ifndef HAVE_SPINLOCKS
! {
! PGSemaphore spinsemas;
!
! spinsemas = (PGSemaphore) (((char *) shmhdr) + shmhdr->freeoffset);
! shmhdr->freeoffset += MAXALIGN(SpinlockSemaSize());
! SpinlockSemaInit(spinsemas);
! Assert(shmhdr->freeoffset <= shmhdr->totalsize);
! }
! #endif
!
! /*
! * Initialize the spinlock used by ShmemAlloc; we have to do this the hard
! * way, too, for the same reasons as above.
*/
ShmemLock = (slock_t *) (((char *) shmhdr) + shmhdr->freeoffset);
shmhdr->freeoffset += MAXALIGN(sizeof(slock_t));
diff --git a/src/backend/storage/lmgr/spin.c b/src/backend/storage/lmgr/spin.c
index 2864790..874e313 100644
*** a/src/backend/storage/lmgr/spin.c
--- b/src/backend/storage/lmgr/spin.c
***************
*** 25,33 ****
--- 25,48 ----
#include "miscadmin.h"
#include "replication/walsender.h"
#include "storage/lwlock.h"
+ #include "storage/pg_sema.h"
#include "storage/spin.h"
+ #ifndef HAVE_SPINLOCKS
+ PGSemaphore SpinlockSemaArray;
+ #endif
+
+ /*
+ * Report the amount of shared memory needed to store semaphores for spinlock
+ * support.
+ */
+ Size
+ SpinlockSemaSize(void)
+ {
+ return SpinlockSemas() * sizeof(PGSemaphoreData);
+ }
+
#ifdef HAVE_SPINLOCKS
/*
*************** SpinlockSemas(void)
*** 51,71 ****
int
SpinlockSemas(void)
{
! int nsemas;
! /*
! * It would be cleaner to distribute this logic into the affected modules,
! * similar to the way shmem space estimation is handled.
! *
! * For now, though, there are few enough users of spinlocks that we just
! * keep the knowledge here.
! */
! nsemas = NumLWLocks(); /* one for each lwlock */
! nsemas += NBuffers; /* one for each buffer header */
! nsemas += max_wal_senders; /* one for each wal sender process */
! nsemas += 30; /* plus a bunch for other small-scale use */
! return nsemas;
}
/*
--- 66,85 ----
int
SpinlockSemas(void)
{
! return NUM_SPINLOCK_SEMAPHORES;
! }
! /*
! * Initialize semaphores.
! */
! extern void
! SpinlockSemaInit(PGSemaphore spinsemas)
! {
! int i;
! for (i = 0; i < NUM_SPINLOCK_SEMAPHORES; ++i)
! PGSemaphoreCreate(&spinsemas[i]);
! SpinlockSemaArray = spinsemas;
}
/*
*************** SpinlockSemas(void)
*** 75,87 ****
void
s_init_lock_sema(volatile slock_t *lock)
{
! PGSemaphoreCreate((PGSemaphore) lock);
}
void
s_unlock_sema(volatile slock_t *lock)
{
! PGSemaphoreUnlock((PGSemaphore) lock);
}
bool
--- 89,103 ----
void
s_init_lock_sema(volatile slock_t *lock)
{
! static int counter = 0;
!
! *lock = (++counter) % NUM_SPINLOCK_SEMAPHORES;
}
void
s_unlock_sema(volatile slock_t *lock)
{
! PGSemaphoreUnlock(&SpinlockSemaArray[*lock]);
}
bool
*************** int
*** 96,102 ****
tas_sema(volatile slock_t *lock)
{
/* Note that TAS macros return 0 if *success* */
! return !PGSemaphoreTryLock((PGSemaphore) lock);
}
#endif /* !HAVE_SPINLOCKS */
--- 112,118 ----
tas_sema(volatile slock_t *lock)
{
/* Note that TAS macros return 0 if *success* */
! return !PGSemaphoreTryLock(&SpinlockSemaArray[*lock]);
}
#endif /* !HAVE_SPINLOCKS */
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index 24c5069..74d7ba2 100644
*** a/src/include/pg_config_manual.h
--- b/src/include/pg_config_manual.h
***************
*** 57,62 ****
--- 57,70 ----
#define NUM_USER_DEFINED_LWLOCKS 4
/*
+ * When we don't have native spinlocks, we use semaphores to simulate them.
+ * Decreasing this value reduces consumption of OS resources; increasing it
+ * may improve performance, but supplying a real spinlock implementation is
+ * probably far better.
+ */
+ #define NUM_SPINLOCK_SEMAPHORES 1024
+
+ /*
* Define this if you want to allow the lo_import and lo_export SQL
* functions to be executed by ordinary users. By default these
* functions are only available to the Postgres superuser. CAUTION:
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index f869cb0..b2605f9 100644
*** a/src/include/storage/s_lock.h
--- b/src/include/storage/s_lock.h
***************
*** 94,104 ****
#ifndef S_LOCK_H
#define S_LOCK_H
- #include "storage/pg_sema.h"
-
#ifdef HAVE_SPINLOCKS /* skip spinlocks if requested */
-
#if defined(__GNUC__) || defined(__INTEL_COMPILER)
/*************************************************************************
* All the gcc inlines
--- 94,101 ----
*************** spin_delay(void)
*** 1032,1038 ****
* to fall foul of kernel limits on number of semaphores, so don't use this
* unless you must! The subroutines appear in spin.c.
*/
! typedef PGSemaphoreData slock_t;
extern bool s_lock_free_sema(volatile slock_t *lock);
extern void s_unlock_sema(volatile slock_t *lock);
--- 1029,1035 ----
* to fall foul of kernel limits on number of semaphores, so don't use this
* unless you must! The subroutines appear in spin.c.
*/
! typedef int slock_t;
extern bool s_lock_free_sema(volatile slock_t *lock);
extern void s_unlock_sema(volatile slock_t *lock);
diff --git a/src/include/storage/spin.h b/src/include/storage/spin.h
index f459b90..b2b1339 100644
*** a/src/include/storage/spin.h
--- b/src/include/storage/spin.h
***************
*** 57,62 ****
--- 57,65 ----
#define SPIN_H
#include "storage/s_lock.h"
+ #ifndef HAVE_SPINLOCKS
+ #include "storage/pg_sema.h"
+ #endif
#define SpinLockInit(lock) S_INIT_LOCK(lock)
***************
*** 69,73 ****
--- 72,82 ----
extern int SpinlockSemas(void);
+ extern Size SpinlockSemaSize(void);
+
+ #ifndef HAVE_SPINLOCKS
+ extern void SpinlockSemaInit(PGSemaphore);
+ extern PGSemaphore SpinlockSemaArray;
+ #endif
#endif /* SPIN_H */
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