(2010/08/17 23:23), Michael Parker wrote:
This is great, but there are issues with QueryPerformanceCounter that I
think ought to be pointed out if you aren't already aware of them. QPC
is horribly unreliable
on some chipsets and, on some systems, when running on multiple cores.
Both issues are decribed in the MS Knowledge Base,
with the chipset problem at [1] and the multicore problem at [2]. In the
latter, pay particular attention to point #4 in the Recommendations
section.
Starting with Vista, QPC will use the newer High Precision Event Timer
[3], if available (which it should be for most systems running Vista or 7),
so this becomes less of an issue. But for XP, which is still going to be
relevant for a few more years at least, this is a big headache. You can
read more about timing issues in the PDF at [4].
If I were going to use this class in a game, I would expect it to take
the recommended precautions on XP. Otherwise, I'd just roll my own using
timeGetTime.
[1] http://support.microsoft.com/kb/274323
[2] http://msdn.microsoft.com/en-us/library/ee417693.aspx
[3] http://en.wikipedia.org/wiki/High_Precision_Event_Timer
[4] (direct PDF link)
http://algo2.iti.kit.edu/wassenberg/timing/timing_pitfalls.pdf
On Tue, Aug 17, 2010 at 7:43 PM, SHOO <[email protected]
<mailto:[email protected]>> wrote:
I made the module of the stopwatch, so I suggest it again here.
I suggested a time handling module that I called std.time before.
Unfortunately itself was not able to contribute to Phobos for the issue
of license. But, an important function was included in it. It is what is
the StopWatch suggested this time.
I have some knowledge about machine control engineering. In the field of
the machine control engineering, the high accuracy time measurement
often plays an important role.
For example, the case wants to perform the measurement of the voltage
with time by millisecond order for feedback control. When it looks like
it, resolution power is not enough by time acquisition such as C's time
function in many cases.
Or the high accuracy time measurement is important in the game
programming, too. Or in benchmark testing, too.
There is std.perf in Phobos as a module with this role now.
However, the module is unlisted, and a license doesn't seem to be a
Boost license, too.
I did not refer Tango at all about this class and examined and made it
in my own hand completely.
Here is the module to suggest this time:
http://ideone.com/TVw1P
# This module is tested by Windows (real) and Ubuntu (virtual PC).
Please look at it once by all means, and review it.
I think that I will commit it at 2010-08-22T15:00Z as far as there is
not serious dissenting opinion.
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Mike Parker
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I have some knowledge about these problems.
However, there is not the tool to measure really correct time by Windows.
It means that Windows have a problem about timeGetTime equally.
Ability of timeGetTime is about 10[ms] order. Besides, its accuracy is
affected by programs to work in background.
In the scene using a highly precise performance counter, the performance
seems to be insufficiency.
I think the problem that QPC has is the defect of OS and machines.
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