> > FWIW, my first X11 game I ever wrote, which was similar to the > game "LodeRunner", used a select() timeout for the timing loop
select(),nanosleep(),poll(),etc all sleep one tick longer _except_ when previous syscall was interrupted by a signal or when input became available. this is due to tvtohz ( sys/kern/kern_clock.c ) allways adding 1 to 'allow for the current tick to expire'. this badly breaks some - maybe poor - code I have written which hooks both i/o polling and timers ( set_fd, set_timer,kill_timer in the style of javascript) on a select() loop. (random timeouts would be better here!) I'm not sure but this seems to affect also the Xkb ( I use to set autorepeat to delay 10,repeat 120 ) when playing my tetris ... why not testing for zero result instead of adding 1 in tvtohz ? if (ticks > INT_MAX) ticks = INT_MAX; + else if (ticks == 0) + ticks = 1; return ((int)ticks); I modified kern_clock.c and other places which assume that tvtohz adds 1 in 4.4 long time ago and recently in 5.0 and haven't seen so far any harm at all. I attached my trivial patch and a little test program. Best regards adi notes: tvtohz has been renamed to hzto in NetBSD but is the same. of course you can write ticks = (sec * hz) + (((unsigned long)usec + (tick - 1)) / tick) ?: 1; but this wouldn't work with other compiler than GCC ( does FreeBSD compile with other compiler anyway ?)
/* select [msec] - display select() timeout inaccuracy as '[+-] sec usec' */ #include <sys/types.h> #include <sys/time.h> #include <sys/sysctl.h> #include <unistd.h> #include <errno.h> #include <signal.h> #include <time.h> #include <err.h> #include <stdio.h> fd_set rdfs; int ms; void sig(int unused) {} int main(int argc,char **argv) { int k,mib[2]; struct timeval tv,savtv,otv; struct clockinfo clock; char buf[256]; signal(SIGQUIT,sig); if (argc > 1) ms = atoi(argv[1]); if (!ms) ms = 500; savtv.tv_usec = ms % 1000 * 1000; savtv.tv_sec = ms / 1000; mib[0] = CTL_KERN; mib[1] = KERN_CLOCKRATE; k = sizeof clock; if (sysctl(mib,2,&clock,&k,NULL,0)) err(1,"sysctl"); printf("%d\n",clock.tick); savtv.tv_usec -= savtv.tv_usec % clock.tick; redo: tv = savtv; gettimeofday(&otv,NULL); for(;;) { FD_SET(0,&rdfs); k = select(1,&rdfs,NULL,NULL,&tv); gettimeofday(&tv,NULL); timersub(&tv,&otv,&tv); switch(k) { case 0: if (timercmp(&tv,&savtv,<)) { timersub(&savtv,&tv,&tv);k = '-'; } else { timersub(&tv,&savtv,&tv);k = '+'; } printf("%c%4d s %10d us\n",k,tv.tv_sec,tv.tv_usec); goto redo; case -1: if (errno != EINTR) err(1,"select"); printf("\t--interrupt\n"); break; default: read(0,buf,256); printf("\t--input\n"); break; } timersub(&savtv,&tv,&tv); if (tv.tv_sec < 0) timerclear(&tv); } } /* use ^M for input and ^\ for interrupt unpatched kernel: + 0 s 9938 us --input + 0 s 9959 us + 0 s 9972 us + 0 s 9930 us ^\ --interrupt + 0 s 9954 us + 0 s 9954 us patched kernel: - 0 s 44 us ^\ --interrupt - 0 s 3 us - 0 s 100 us --input - 0 s 44 us - 0 s 47 us (this on xterm,on console results are better) */
diff -Naur osrc/sys/kern/kern_clock.c src/sys/kern/kern_clock.c --- osrc/sys/kern/kern_clock.c Tue Nov 19 23:58:52 2002 +++ src/sys/kern/kern_clock.c Mon Dec 2 23:47:36 2002 @@ -257,8 +257,7 @@ * If the number of usecs in the whole seconds part of the time * difference fits in a long, then the total number of usecs will * fit in an unsigned long. Compute the total and convert it to - * ticks, rounding up and adding 1 to allow for the current tick - * to expire. Rounding also depends on unsigned long arithmetic + * ticks. Rounding also depends on unsigned long arithmetic * to avoid overflow. * * Otherwise, if the number of ticks in the whole seconds part of @@ -291,14 +290,15 @@ ticks = 1; } else if (sec <= LONG_MAX / 1000000) ticks = (sec * 1000000 + (unsigned long)usec + (tick - 1)) - / tick + 1; + / tick; else if (sec <= LONG_MAX / hz) - ticks = sec * hz - + ((unsigned long)usec + (tick - 1)) / tick + 1; + ticks = sec * hz + ((unsigned long)usec + (tick - 1)) / tick; else ticks = LONG_MAX; if (ticks > INT_MAX) ticks = INT_MAX; + else if (ticks == 0) + ticks = 1; return ((int)ticks); } diff -Naur osrc/sys/kern/kern_time.c src/sys/kern/kern_time.c --- osrc/sys/kern/kern_time.c Tue Dec 3 00:14:05 2002 +++ src/sys/kern/kern_time.c Mon Dec 2 23:33:04 2002 @@ -527,10 +527,6 @@ * Else compute next time timer should go off which is > current time. * This is where delay in processing this timeout causes multiple * SIGALRM calls to be compressed into one. - * tvtohz() always adds 1 to allow for the time until the next clock - * interrupt being strictly less than 1 clock tick, but we don't want - * that here since we want to appear to be in sync with the clock - * interrupt even when we're delayed. */ void realitexpire(void *arg) @@ -555,7 +551,7 @@ if (timevalcmp(&p->p_realtimer.it_value, &ctv, >)) { ntv = p->p_realtimer.it_value; timevalsub(&ntv, &ctv); - callout_reset(&p->p_itcallout, tvtohz(&ntv) - 1, + callout_reset(&p->p_itcallout, tvtohz(&ntv), realitexpire, p); splx(s); PROC_UNLOCK(p); diff -Naur osrc/sys/kern/kern_timeout.c src/sys/kern/kern_timeout.c --- osrc/sys/kern/kern_timeout.c Thu Sep 5 14:42:03 2002 +++ src/sys/kern/kern_timeout.c Mon Dec 2 23:56:45 2002 @@ -399,15 +399,17 @@ return; else if (time_change->tv_sec <= LONG_MAX / 1000000) delta_ticks = (time_change->tv_sec * 1000000 + - time_change->tv_usec + (tick - 1)) / tick + 1; + time_change->tv_usec + (tick - 1)) / tick; else if (time_change->tv_sec <= LONG_MAX / hz) delta_ticks = time_change->tv_sec * hz + - (time_change->tv_usec + (tick - 1)) / tick + 1; + (time_change->tv_usec + (tick - 1)) / tick; else delta_ticks = LONG_MAX; if (delta_ticks > INT_MAX) delta_ticks = INT_MAX; + else if (delta_ticks == 0) + delta_ticks = 1; /* * Now rip through the timer calltodo list looking for timers diff -Naur osrc/sys/net/bpf.c src/sys/net/bpf.c --- osrc/sys/net/bpf.c Tue Nov 19 23:58:58 2002 +++ src/sys/net/bpf.c Mon Dec 2 23:58:24 2002 @@ -774,12 +774,8 @@ { struct timeval *tv = (struct timeval *)addr; - /* - * Subtract 1 tick from tvtohz() since this isn't - * a one-shot timer. - */ if ((error = itimerfix(tv)) == 0) - d->bd_rtout = tvtohz(tv) - 1; + d->bd_rtout = tvtohz(tv); break; }