How would you make accurate time measurements using Lua ?

[Roland_Yonaba]

Hi folks,

I was wondering how one could make some accurate time measurements ?
My question Lua-related, not Löve related, or i'll just use love.timer.

Say, for instance, that I'll need to benchmark the execution time of function.
Problem is, Lua's operating system facilities offers me os.clock, os.difftime, os.time, but they all works with seconds.
What if i need milliseconds, or less ?
Is there some hacky stuff, or should I rely on external libs ?

Thanks in advance.

[Boolsheet]

os.clock is in seconds, but usually has millisecond precision. The C standard says it should be the best CPU time approximation and Linux-based stuff (and OS X, I think) does this just fine. Windows returns realtime instead. It can be used to do benchmarking, but you should not compare the results across platforms.

If you need microsecond precision, you have to reach out to the OS API. I made myself a little module for this. Should work on Windows and Linux (link against librt if monotonic timers are available). I don't have OS X so I didn't implement its monotonic timer, but the gettimeofday function is available there.

Code: Select all

#ifdef _WIN32
	#include <Windows.h>
	#define EXPORT_DECL __declspec(dllexport)
#else
	#include <time.h>
	#include <sys/time.h>
	#define EXPORT_DECL
#endif

#include <lua.h>

#ifdef _WIN32
static double timer_resolution = 0.0;
#endif

static int microtime_query(lua_State * L)
{
	lua_Number time = 0;

#ifdef _WIN32
	LARGE_INTEGER counter;
	QueryPerformanceCounter(&counter);
	time = (lua_Number)(counter.QuadPart * timer_resolution);
#elif _POSIX_TIMERS > 0 && defined(_POSIX_MONOTONIC_CLOCK) && defined(CLOCK_MONOTONIC_RAW) || defined(CLOCK_MONOTONIC)
	struct timespec t;
	#ifdef CLOCK_MONOTONIC_RAW
	clock_gettime(CLOCK_MONOTONIC_RAW, &t);
	#else
	clock_gettime(CLOCK_MONOTONIC, &t);
	#endif
	time = (lua_Number)((double)t.tv_sec + (double)t.tv_nsec / 1000000000.0);
#else
	struct timeval t;
	gettimeofday(&t, NULL);
	time = (lua_Number)((double)t.tv_sec + (double)t.tv_usec / 1000000.0);
#endif

	lua_pushnumber(L, time);
	return 1;
}

EXPORT_DECL int luaopen_microtime(lua_State * L)
{
#ifdef _WIN32
	LARGE_INTEGER frequency;
	int support = QueryPerformanceFrequency(&frequency);
	if (!support)
	{
		// No high-resolution counter found.
		lua_pushnil(L);
		return 1;
	}

	timer_resolution = 1.0 / frequency.QuadPart;
#endif

	lua_pushcfunction(L, &microtime_query);
	return 1;
}

This is just for getting the value of a timer with an undefined starting time. There may be more advanced timer Lua modules out there. LuaSocket also has a realtime timer with millisecond precision if that's already part of your script.

[Roland_Yonaba]

Wow.
Gratitutes, Boolean dude.

Yes, I've been digging in the mid-time. I was more looking for some tool in plain Lua, but it seems there isn't.
Thanks for the C-snippet, and for the LuaSocket tip.

[Inny]

This doesn't work for you?

https://love2d.org/wiki/love.timer.getMicroTime

Edit: Sorry, I didn't realize that this was about Lua and not Love.