package/busybox/patches/000-upstream-hwclock.patch

   1 --- a/util-linux/hwclock.c
   2 +++ b/util-linux/hwclock.c
   3 @@ -109,10 +109,53 @@ static void to_sys_clock(const char **pp
   4
   5  static void from_sys_clock(const char **pp_rtcname, int utc)
   6  {
   7 -#define TWEAK_USEC 200
   8 -       struct tm tm_time;
   9 +#if 1
  10         struct timeval tv;
  11 +       struct tm tm_time;
  12 +       int rtc;
  13 +
  14 +       rtc = rtc_xopen(pp_rtcname, O_WRONLY);
  15 +       gettimeofday(&tv, NULL);
  16 +       /* Prepare tm_time */
  17 +       if (sizeof(time_t) == sizeof(tv.tv_sec)) {
  18 +               if (utc)
  19 +                       gmtime_r((time_t*)&tv.tv_sec, &tm_time);
  20 +               else
  21 +                       localtime_r((time_t*)&tv.tv_sec, &tm_time);
  22 +       } else {
  23 +               time_t t = tv.tv_sec;
  24 +               if (utc)
  25 +                       gmtime_r(&t, &tm_time);
  26 +               else
  27 +                       localtime_r(&t, &tm_time);
  28 +       }
  29 +#else
  30 +/* Bloated code which tries to set hw clock with better precision.
  31 + * On x86, even though code does set hw clock within <1ms of exact
  32 + * whole seconds, apparently hw clock (at least on some machines)
  33 + * doesn't reset internal fractional seconds to 0,
  34 + * making all this a pointless excercise.
  35 + */
  36 +       /* If we see that we are N usec away from whole second,
  37 +        * we'll sleep for N-ADJ usecs. ADJ corrects for the fact
  38 +        * that CPU is not infinitely fast.
  39 +        * On infinitely fast CPU, next wakeup would be
  40 +        * on (exactly_next_whole_second - ADJ). On real CPUs,
  41 +        * this difference between current time and whole second
  42 +        * is less than ADJ (assuming system isn't heavily loaded).
  43 +        */
  44 +       /* Small value of 256us gives very precise sync for 2+ GHz CPUs.
  45 +        * Slower CPUs will fail to sync and will go to bigger
  46 +        * ADJ values. qemu-emulated armv4tl with ~100 MHz
  47 +        * performance ends up using ADJ ~= 4*1024 and it takes
  48 +        * 2+ secs (2 tries with successively larger ADJ)
  49 +        * to sync. Even straced one on the same qemu (very slow)
  50 +        * takes only 4 tries.
  51 +        */
  52 +#define TWEAK_USEC 256
  53         unsigned adj = TWEAK_USEC;
  54 +       struct tm tm_time;
  55 +       struct timeval tv;
  56         int rtc = rtc_xopen(pp_rtcname, O_WRONLY);
  57
  58         /* Try to catch the moment when whole second is close */
  59 @@ -124,55 +167,64 @@ static void from_sys_clock(const char **
  60
  61                 t = tv.tv_sec;
  62                 rem_usec = 1000000 - tv.tv_usec;
  63 -               if (rem_usec < 1024) {
  64 -                       /* Less than 1ms to next second. Good enough */
  65 +               if (rem_usec < adj) {
  66 +                       /* Close enough */
  67   small_rem:
  68                         t++;
  69                 }
  70
  71 -               /* Prepare tm */
  72 +               /* Prepare tm_time from t */
  73                 if (utc)
  74                         gmtime_r(&t, &tm_time); /* may read /etc/xxx (it takes time) */
  75                 else
  76                         localtime_r(&t, &tm_time); /* same */
  77 -               tm_time.tm_isdst = 0;
  78 +
  79 +               if (adj >= 32*1024) {
  80 +                       break; /* 32 ms diff and still no luck?? give up trying to sync */
  81 +               }
  82
  83                 /* gmtime/localtime took some time, re-get cur time */
  84                 gettimeofday(&tv, NULL);
  85
  86 -               if (tv.tv_sec < t /* may happen if rem_usec was < 1024 */
  87 -                || (tv.tv_sec == t && tv.tv_usec < 1024)
  88 +               if (tv.tv_sec < t /* we are still in old second */
  89 +                || (tv.tv_sec == t && tv.tv_usec < adj) /* not too far into next second */
  90                 ) {
  91 -                       /* We are not too far into next second. Good. */
  92 -                       break;
  93 -               }
  94 -               adj += 32; /* 2^(10-5) = 2^5 = 32 iterations max */
  95 -               if (adj >= 1024) {
  96 -                       /* Give up trying to sync */
  97 -                       break;
  98 +                       break; /* good, we are in sync! */
  99                 }
 100
 101 -               /* Try to sync up by sleeping */
 102                 rem_usec = 1000000 - tv.tv_usec;
 103 -               if (rem_usec < 1024) {
 104 -                       goto small_rem; /* already close, don't sleep */
 105 +               if (rem_usec < adj) {
 106 +                       t = tv.tv_sec;
 107 +                       goto small_rem; /* already close to next sec, don't sleep */
 108                 }
 109 -               /* Need to sleep.
 110 -                * Note that small adj on slow processors can make us
 111 -                * to always overshoot tv.tv_usec < 1024 check on next
 112 -                * iteration. That's why adj is increased on each iteration.
 113 -                * This also allows it to be reused as a loop limiter.
 114 -                */
 115 -               usleep(rem_usec - adj);
 116 -       }
 117
 118 -       xioctl(rtc, RTC_SET_TIME, &tm_time);
 119 +               /* Try to sync up by sleeping */
 120 +               usleep(rem_usec - adj);
 121
 122 -       /* Debug aid to find "good" TWEAK_USEC.
 123 +               /* Jump to 1ms diff, then increase fast (x2): EVERY loop
 124 +                * takes ~1 sec, people won't like slowly converging code here!
 125 +                */
 126 +       //bb_error_msg("adj:%d tv.tv_usec:%d", adj, (int)tv.tv_usec);
 127 +               if (adj < 512)
 128 +                       adj = 512;
 129 +               /* ... and if last "overshoot" does not look insanely big,
 130 +                * just use it as adj increment. This makes convergence faster.
 131 +                */
 132 +               if (tv.tv_usec < adj * 8) {
 133 +                       adj += tv.tv_usec;
 134 +                       continue;
 135 +               }
 136 +               adj *= 2;
 137 +       }
 138 +       /* Debug aid to find "optimal" TWEAK_USEC with nearly exact sync.
 139          * Look for a value which makes tv_usec close to 999999 or 0.
 140 -        * for 2.20GHz Intel Core 2: TWEAK_USEC ~= 200
 141 +        * For 2.20GHz Intel Core 2: optimal TWEAK_USEC ~= 200
 142          */
 143 -       //bb_error_msg("tv.tv_usec:%d adj:%d", (int)tv.tv_usec, adj);
 144 +       //bb_error_msg("tv.tv_usec:%d", (int)tv.tv_usec);
 145 +#endif
 146 +
 147 +       tm_time.tm_isdst = 0;
 148 +       xioctl(rtc, RTC_SET_TIME, &tm_time);
 149
 150         if (ENABLE_FEATURE_CLEAN_UP)
 151                 close(rtc);