Re: [Algorithms] Timing problems

[Dan W. <Da...@Pi...>]

We stuck the SetThreadAffinityMask code in our libraries, and our timing
problems went away.
 
However, about 6 mo later, we ended up with a weird bug: 
 
We have a converter that run as part of our build process.  To speed up
the build, we started running multiple instances of the converter on a
multicore machine.  However, the build times didn't go down, and closer
examination showed that only one CPU use being used.  
 
Turns out SetThreadAffinityMask was doing exactly what it was supposed
to and making all our processes run on one core. Our solution was to
look at the processor identifier and skip the affinity business CPU's we
know to work correctly.
 
-D

________________________________

From: Paul at Home [mailto:pa...@ru...] 
Sent: Sunday, January 04, 2009 8:32 AM
To: Game Development Algorithms
Subject: Re: [Algorithms] Timing problems


Thanks Emil, I'll give that a go first. :)

Regards,
Paul Johnson.
 
 

	----- Original Message ----- 
	From: Emil Persson <mailto:hu...@co...>  
	To: 'Game Development Algorithms'
<mailto:gda...@li...>  
	Sent: Sunday, January 04, 2009 2:36 PM
	Subject: Re: [Algorithms] Timing problems


	The problem doesn't arise from threading your application, but
from calling QPC from different CPUs. In a multi-core machine Windows
will schedule each thread to run on any CPU as it sees fit. First
time-slice for your application may run on CPU0, the next one perhaps on
CPU2, and then CPU1 etc. By the time you're reading QPC you could be on
any CPU and it could be different cores every frame. Unless of course
you call SetThreadAffinityMask(). Something like this at the beginning
of the application should do:

	SetThreadAffinityMask(GetCurrentThread(), 1);

	 

	This will stick the thread to CPU 0. 

	 

	-Emil

	 

	 

	From: Paul at Home [mailto:pa...@ru...] 
	Sent: 04 January 2009 12:44
	To: Game Development Algorithms
	Subject: Re: [Algorithms] Timing problems

	 

	I've seen this around but I'm not using any threads. Not
deliberately anyway. Do you put a zero in for "me" ?

	
	Regards,
	Paul Johnson.

	 

	 

		----- Original Message ----- 

		From: Gregory Junker <mailto:gj...@da...>  

		To: 'Game Development Algorithms'
<mailto:gda...@li...>  

		Sent: Sunday, January 04, 2009 2:07 AM

		Subject: Re: [Algorithms] Timing problems

		 

		Hi Paul

		 

		By "jump problem", do you mean this?

		 

		http://support.microsoft.com/kb/274323

		 

		 

		Either way, simply set the thread that is your time
master to run on only a single core, using SetThreadAffinityMask() (on
Win32, of course - not sure what the equivalent, if any, might be on
Linux). 

		 

	
http://msdn.microsoft.com/en-us/library/ms686247(VS.85).aspx

		 

		 

		Yes, it's a hack, but at present, it's what we got. ;)

		
		Greg

		 

________________________________

		From: Paul at Home [mailto:pa...@ru...] 
		Sent: Saturday, January 03, 2009 3:06 PM
		To: gda...@li...
		Subject: [Algorithms] Timing problems

		 

		I've just fallen foul of QPC not working correctly
having just gone from a single processor to a quad core.

		 

		I remember reading somewhere that multiple processors
could cause problems in the future, but I guess the future (for me) just
arrived. I do handle the well-known "jump" problem but I guess that's
old news now anyway.

		 

		Can anyone point me in the right direction for how to
fix this please ?

		
		Regards,
		Paul Johnson.

		 

		 

________________________________

	
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