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Implement a 'busywait' cvar to force the client and server to busy wait.

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Sleeping with Sys_Nanosleep() is fair enough but has the problem that we
may get scheduled away and the hosts power management inteferes with our
interal timings. While this wasn't a big issue on FreeBSD and Linux it
let to serious timing issues in Windows.

There're several reports in the net, apperently everything below 5ms is
very inaccurate on Windows:
* https://stackoverflow.com/questions/7827062/ \
   is-there-a-windows-equivalent-of-nanosleep/7827446#7827446
* https://lists.gnu.org/archive/html/bug-gnulib/2010-04/msg00045.html
This commit is contained in:
Yamagi Burmeister 2018-02-12 18:12:48 +01:00
parent 832f3f6497
commit b80ff7f40c
1 changed files with 32 additions and 4 deletions
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36
src/common/frame.c
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@ -34,6 +34,7 @@ cvar_t *timescale;
cvar_t *fixedtime;
cvar_t *cl_maxfps;
cvar_t *dedicated;
cvar_t *busywait;
extern cvar_t *logfile_active;
extern jmp_buf abortframe; /* an ERR_DROP occured, exit the entire frame */
@ -129,6 +130,12 @@ Qcommon_Buildstring(void)
printf("Architecture: %s\n", YQ2ARCH);
}
#ifndef DEDICATED_ONLY
#define FRAMEDELAY 5
#else
#define FRAMEDELAY 850
#endif
void
Qcommon_Mainloop(void)
{
@ -139,12 +146,32 @@ Qcommon_Mainloop(void)
while (1)
{
// Throttle the game a little bit.
#ifdef DEDICATED_ONLY
Sys_Nanosleep(850000);
#else
Sys_Nanosleep(5000);
if (busywait->value)
{
long long spintime = Sys_Microseconds();
while (1)
{
#if defined (__GNUC__) && (__i386 || __x86_64__)
/* Give the CPU a hint that this is a very tight
spinloop. One PAUSE instruction each loop is
enough to reduce power consumption and head
dispersion a lot, it's 95°C against 67°C on
a Kaby Lake laptop. */
asm("pause");
#endif
if (Sys_Microseconds() - spintime >= FRAMEDELAY)
{
break;
}
}
}
else
{
Sys_Nanosleep(FRAMEDELAY * 1000);
}
newtime = Sys_Microseconds();
Qcommon_Frame(newtime - oldtime);
oldtime = newtime;
@ -226,6 +253,7 @@ Qcommon_Init(int argc, char **argv)
host_speeds = Cvar_Get("host_speeds", "0", 0);
log_stats = Cvar_Get("log_stats", "0", 0);
showtrace = Cvar_Get("showtrace", "0", 0);
busywait = Cvar_Get("busywait", "1", CVAR_ARCHIVE);
#else
dedicated = Cvar_Get("dedicated", "1", CVAR_NOSET);
#endif