Re: [boost] Re: Re: Re: Re: Profiling Library suggestion

From: christopher diggins (cdiggins_at_[hidden])
Date: 2005-02-13 19:30:01

----- Original Message ----- 
From: "Martin Slater" <mslater_at_[hidden]>
>>
> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/winui/windowsuserinterface/windowing/timers/timerreference/timerfunctions/queryperformancecounter.asp
>
> watch the line wrap. QueryPerformanceCounter uses the CPU clock and is not 
> per task but system wide.

Thanks.

>> Can you point me to documentation which supports your assertion?
>>
>>> The only problem with QueryPerformanceCounter() is that it can "jump"
>>> on some chipsets.
>>
>>
>> I believe this problem is perhaps not restricted to 
>> QueryPerformanceCounter() but to any counter counting mechanism, as the 
>> problem is at the chipset level not the API level.
>
> No, there is a very particualar problem relating to 
> QueryPerformanceCounter() on some (old?) chipsets the can cause it go 
> backwards in time and wrap after approximately 20 minutes. I reported this 
> to microsoft some years ago and it was confirmed an issue. (at the time 
> only happened to me on one particualar celeron / motherboard 
> configuration). By backwards in time I mean you could call the counter in 
> a loop and have a reported time earlier than one got the previous 
> iteration.

Really? That is different than the issue documentation I found at 
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q274323 which stats 
that the QueryPerformanceCounter() can jump *ahead* a few seconds. I wonder 
if the status of the issue has changed to this new version or the 
documentation just sux.

> This bit me on commercial code and I resorted to
>    timeBeginPeriod(1);
>    timeGetTime();
> instead with no issues.
>
> Martin

Thanks for your help Martin,
Christopher