db2/os/os_spin.c

   1 /*-
   2  * See the file LICENSE for redistribution information.
   3  *
   4  * Copyright (c) 1997, 1998
   5  *      Sleepycat Software.  All rights reserved.
   6  */
   7
   8 #include "config.h"
   9
  10 #ifndef lint
  11 static const char sccsid[] = "@(#)os_spin.c     10.10 (Sleepycat) 10/12/98";
  12 #endif /* not lint */
  13
  14 #ifndef NO_SYSTEM_INCLUDES
  15 #include <sys/types.h>
  16 #if defined(HAVE_PSTAT_GETDYNAMIC)
  17 #include <sys/pstat.h>
  18 #endif
  19
  20 #include <limits.h>
  21 #include <unistd.h>
  22 #endif
  23
  24 #include "db_int.h"
  25 #include "os_jump.h"
  26
  27 #if defined(HAVE_PSTAT_GETDYNAMIC)
  28 /*
  29  * __os_pstat_getdynamic --
  30  *      HP/UX.
  31  */
  32 static int
  33 __os_pstat_getdynamic()
  34 {
  35         struct pst_dynamic psd;
  36
  37         return (pstat_getdynamic(&psd,
  38             sizeof(psd), (size_t)1, 0) == -1 ? 1 : psd.psd_proc_cnt);
  39 }
  40 #endif
  41
  42 #if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
  43 /*
  44  * __os_sysconf --
  45  *      Solaris, Linux.
  46  */
  47 static int
  48 __os_sysconf(void)
  49 {
  50         int nproc;
  51
  52         return ((nproc = sysconf(_SC_NPROCESSORS_ONLN)) > 1 ? nproc : 1);
  53 }
  54 #endif
  55
  56 /*
  57  * __os_spin --
  58  *      Return the number of default spins before blocking.
  59  *
  60  * PUBLIC: int __os_spin __P((void));
  61  */
  62 int
  63 __os_spin()
  64 {
  65         /*
  66          * If the application specified a value or we've already figured it
  67          * out, return it.
  68          *
  69          * XXX
  70          * We don't want to repeatedly call the underlying function because
  71          * it can be expensive (e.g., requiring multiple filesystem accesses
  72          * under Debian Linux).
  73          */
  74         if (DB_GLOBAL(db_tsl_spins) != 0)
  75                 return (DB_GLOBAL(db_tsl_spins));
  76
  77         DB_GLOBAL(db_tsl_spins) = 1;
  78 #if defined(HAVE_PSTAT_GETDYNAMIC)
  79         DB_GLOBAL(db_tsl_spins) = __os_pstat_getdynamic();
  80 #endif
  81 #if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
  82         DB_GLOBAL(db_tsl_spins) = __os_sysconf();
  83 #endif
  84
  85         /*
  86          * Spin 50 times per processor, we have anecdotal evidence that this
  87          * is a reasonable value.
  88          */
  89         DB_GLOBAL(db_tsl_spins) *= 50;
  90
  91         return (DB_GLOBAL(db_tsl_spins));
  92 }
  93
  94 /*
  95  * __os_yield --
  96  *      Yield the processor.
  97  *
  98  * PUBLIC: void __os_yield __P((u_long));
  99  */
 100 void
 101 __os_yield(usecs)
 102         u_long usecs;
 103 {
 104         if (__db_jump.j_yield != NULL && __db_jump.j_yield() == 0)
 105                 return;
 106         __os_sleep(0, usecs);
 107 }