RE: Re[4]: [GD-Windows] Performance timing

[Jon W. <hp...@mi...>]

That's interesting!

As others have said: the accuracy of GetTickCount() varies highly depending
on your system in general, as it polls some variable that gets updated once
in a while; that's why it's the fastest. For a FPS counter, it's probably
accurate enough.

When you run micro-benchmarks like this, 10,000 calls might not be enough.
Get interrupted once by a task switch, or just network packet/mouse
movement, and your measurement is off. That's why I prefer measuring the
BEST sample out of many samples. That, for RDTSC, is on the order of 40
cycles, if you don't care about temporal serialization (which you typically
don't).

Hard to say more without more details about the benchmark, though. (I've
been burned by benchmarks measuring something other than I thought they did
SOOO many times it's not even funny anymore).

Cheers,

			/ h+


-----Original Message-----
From: gam...@li...
[mailto:gam...@li...]On Behalf Of
Carl Bevil
Sent: Tuesday, February 10, 2004 5:27 PM
To: Simon O'Connor
Subject: Re[4]: [GD-Windows] Performance timing


Did that, and they have a nice utility that performs some timing tests on
your machine and spits out a report (it's at
http://developer.nvidia.com/object/timer_function_performance.html).

The report had interesting results:

-----

QueryPerformanceFrequency() freq  = 0  2593560000


method 0:
  QueryPerfCntr..()  10000 times
  tot:   0 6720740
  avg:   672.074000
  avg time:			 2.59132e-007


method 1:
  GetTickCount()  10000 times
  tot:   0 260708
  avg:   26.070800
  avg time:			 1.00521e-008


method 2:
  TimeGetTime()  10000 times
  tot:   0 1420712
  avg:   142.071200
  avg time:			 5.47785e-008



method 3:
  Pentium internal high-freq cntr()  10000 times
  tot:   0 840856
  avg:   84.085600
  avg time:			 3.24209e-008

-----

I've left out the data for less than 10,000 iterations for sake of length;
the averages were similar for these cases (and I ran the test a couple times
with similar results).

It looks like GetTickCount is the fastest, at least for this test setup on
my machine.  Am I reading the results wrong?  I would have expected RDTSC to
be the fastest.  What could this mean?  Is this because of the cache effects
that Jon mentioned?  Just curious.  :-)

Tbanks!

Carl


------------------------------------------
Tuesday, February 10, 2004, 4:44:01 PM, you wrote:


> Hi Carl,


> Have a search around nVidia's developer website
> (http://developer.nvidia.com), IIRC they did presentation surveying each
of
> the major timing methods with regard to using them to profile code and the
> advantages and disadvantages plus latencies of each.



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