Can I ask where this was left? > Hi, > > I've managed to speak to someone knowledgeable at Digital in the UK > who pointed me in the direction of a very interesting include file for > Digital C/C++, namely /usr/include/alpha/builtins.h. > > It contains a series of function prototypes which are then converted > into fast assembler sequences by the compiler. In particular a number > of these seem highly suited for the task of rewriting the alpha > spinlock code avoiding IPC semaphores. > > Amongst the many functions I believe the most relevant are, for the > TAS() macro in s_lock.h: > > /* > ** Interlocked "test for bit set and then set". Returns non-zero > ** if bit was already set. > */ > int __INTERLOCKED_TESTBITSS_QUAD(volatile void *__address, int __bit_position); > int __INTERLOCKED_TESTBITSS_QUAD_RETRY(volatile void *__address, > int __bit_position, > int __retry, > int *__status); > > Note that this call does _not_ generate a memory barrier. For the > others, i.e. S_LOCK and S_UNLOCK perhaps the following might help: > > /* > ** Acquire/release binary spinlock based on low-order bit of a longword. > ** NOTE: Memory barrier generated after lock, before unlock. > ** _RETRY variant returns non-zero on success within retry attempts. > */ > void __LOCK_LONG(volatile void *__address); > int __LOCK_LONG_RETRY(volatile void *__address, int __retry); > void __UNLOCK_LONG(volatile void *__address); > > There are also counting semaphores if need be (all in the same file). > If we change s_lock from msemaphore to long then the following patch > compiles and is being tested by Adriaan Joubert as we speak. It > probably crashes & burns but at least we can see if we get anywhere. > My personal opinion is that it might be the way to go, I haven't > looked carefully at S_LOCK etc. but will do so once Adriaan has > crashed the copy of Postgres currently being compiled. > > ===File ~/src/hacks/s_lock.diff===================== > --- s_lock.h.orig Wed Jun 14 15:33:28 2000 > +++ s_lock.h Wed Jun 14 16:11:29 2000 > @@ -252,10 +252,18 @@ > * Note that slock_t on the Alpha AXP is msemaphore instead of char > * (see storage/ipc.h). > */ > -#define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0) > -#define S_UNLOCK(lock) msem_unlock((lock), 0) > -#define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED) > -#define S_LOCK_FREE(lock) (!(lock)->msem_state) > +#if 0 > +/* Original hack */ > +# define TAS(lock) (msem_lock((lock), MSEM_IF_NOWAIT) < 0) > +# define S_UNLOCK(lock) msem_unlock((lock), 0) > +# define S_INIT_LOCK(lock) msem_init((lock), MSEM_UNLOCKED) > +# define S_LOCK_FREE(lock) (!(lock)->msem_state) > +#else > +/* Arrigo's hack */ > +# include <alpha/builtins.h> > +# define TAS(lock) (__INTERLOCKED_TESTBITSS_QUAD(lock,0)) > +#endif > + > > #else /* i.e. not __osf__ */ > > ============================================================ > > Ciao, > > Arrigo > > P.S. Yes, I don't really know what I am doing but trying my best to > learn ;-) > -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
