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Clocksource: use a better clock if available.

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clock_gettime() is a far better clock than gettimeofday().

Even better than clock_gettime() is that you can select either
CLOCK_MONOTONIC, or even CLOCK_MONOTONIC_RAW. These clocks offer
high precision time. And the _RAW variant will never roll back
due to NTP drift or daylight savings, or otherwise.

I've adjusted this code to select the right clock method auto-
matically based on what's available in the OS. This means that
if you're running a very old linux version, MacOS or other,
you will automatically get the best clocksource available.

I've tested all Linux clocksources by selectively compiling and
running a 10k+ timer test suite. In all cases I confirmed that
the 3 POSIX Linux clocksources worked properly, and were
selected properly.

I've modified the OS X compile path to use the high-res clock
source for all time functions, but I can't confirm it works or
that it compiles.

As for WIN32, I confirmed that the used clocksource is indeed
a Monotonic clocksource, so good news: that code section appears
to be exactly what it should be.
This commit is contained in:
Auke Kok 2016-01-23 23:06:26 -08:00 • committed by ShadowNinja
parent 860d70bd0e
commit 4ac1e9bccb
2 changed files with 42 additions and 29 deletions
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69
src/porting.h
View file

@ -211,33 +211,11 @@ void initIrrlicht(irr::IrrlichtDevice * );
}
#else // Posix
inline u32 getTimeS()
inline void _os_get_clock(struct timespec *ts)
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec;
}
inline u32 getTimeMs()
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec * 1000 + tv.tv_usec / 1000;
}
inline u32 getTimeUs()
{
struct timeval tv;
gettimeofday(&tv, NULL);
return tv.tv_sec * 1000000 + tv.tv_usec;
}
inline u32 getTimeNs()
{
struct timespec ts;
// from http://stackoverflow.com/questions/5167269/clock-gettime-alternative-in-mac-os-x
#if defined(__MACH__) && defined(__APPLE__) // OS X does not have clock_gettime, use clock_get_time
#if defined(__MACH__) && defined(__APPLE__)
// from http://stackoverflow.com/questions/5167269/clock-gettime-alternative-in-mac-os-x
// OS X does not have clock_gettime, use clock_get_time
clock_serv_t cclock;
mach_timespec_t mts;
host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
@ -245,9 +223,44 @@ void initIrrlicht(irr::IrrlichtDevice * );
mach_port_deallocate(mach_task_self(), cclock);
ts.tv_sec = mts.tv_sec;
ts.tv_nsec = mts.tv_nsec;
#elif defined(CLOCK_MONOTONIC_RAW)
clock_gettime(CLOCK_MONOTONIC_RAW, ts);
#elif defined(_POSIX_MONOTONIC_CLOCK)
clock_gettime(CLOCK_MONOTONIC, ts);
#else
clock_gettime(CLOCK_REALTIME, &ts);
#endif
struct timeval tv;
gettimeofday(&tv, NULL);
TIMEVAL_TO_TIMESPEC(&tv, ts);
#endif // defined(__MACH__) && defined(__APPLE__)
}
// Note: these clock functions do not return wall time, but
// generally a clock that starts at 0 when the process starts.
inline u32 getTimeS()
{
struct timespec ts;
_os_get_clock(&ts);
return ts.tv_sec;
}
inline u32 getTimeMs()
{
struct timespec ts;
_os_get_clock(&ts);
return ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
}
inline u32 getTimeUs()
{
struct timespec ts;
_os_get_clock(&ts);
return ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
}
inline u32 getTimeNs()
{
struct timespec ts;
_os_get_clock(&ts);
return ts.tv_sec * 1000000000 + ts.tv_nsec;
}