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Answer 1

+3 A:

Actually, your application will not use more than one CPU unless you specifically do something to utilize more CPUs. If you use the thread pool and/or start additional threads you may use additional available cores, but otherwise your application will just have one thread per default and thus only use one CPU.

Brian Rasmussen 2009-06-27 07:14:21

My application will use more than one CPU because it recording through Windows Media Encoder and do real time encoding to wmv format -- I have tested it and seen all CPU resources are occupied from Windows task manager.Any ideas how to set CPU affinity?

George2 2009-06-27 07:21:17

@Brian: It may still make sense to force a thread to remain on one core, for those systems where the cache is per-core.

mghie 2009-06-27 07:33:56

@mghie, I agree with you. Any ideas for my problem?

George2 2009-06-27 07:39:34

@George2: Well, see my answer, read the MSDN documentation how to use the functions, and call them using platform invoke.

mghie 2009-06-27 07:44:23

Cool, @mghie, please see my reply, I like your answer.

George2 2009-06-27 07:46:06

Answer 2

+7 A:

Go to Task Manager -> Processes tab.
Look for your program. Right click on it.
Select Set Affinity and uncheck one of the checkboxes.

This should free up one processor for you.

For doing it from the code you can add this statement:

System.Diagnostics.Process.GetCurrentProcess().ProcessorAffinity = (System.IntPtr) 1;

Cheers!

Gaurav 2009-06-27 07:25:47

Any programming or configuration ways? I do not want end user to do this each time. :-)

George2 2009-06-27 07:38:52

Try this:System.Diagnostics.Process.GetCurrentProcess().ProcessorAffinity = 1;

Gaurav 2009-06-27 07:47:21

BTW: To use second set it to 2 and to use both cores you can set the value to 3 :)

Gaurav 2009-06-27 07:48:29

System.Diagnostics.Process.GetCurrentProcess().ProcessorAffinity = (System.IntPtr)1;forgot the typecasting laste time :P

Gaurav 2009-06-27 07:49:56

@Gaurav: If you add this to the answer I'll upvote it.

mghie 2009-06-27 07:56:23

@mghie: done :-)

Gaurav 2009-06-27 08:06:16

@Gaurav: Done :-)

mghie 2009-06-27 08:09:38

@Gaurav, why use IntPrt, why not use int?

George2 2009-06-27 08:18:28

Answer 3

+1 A:

The Windows API functions to do this are SetProcessAffinityMask() and SetThreadAffinityMask(). I don't know .NET so I can't say whether there are wrappers around those functions, but this seems to suggest otherwise.

BTW: I agree that these are necessary only in very specific circumstances, it's normally best to let the OS scheduler deal with it. It's one of those questions where you probably shouldn't do it if you have to ask how.

mghie 2009-06-27 07:30:26

@mghie, in my problem, 1. I think I should call SetProcessAffinityMask other than SetThreadAffinityMask, correct? 2. Could I call SetProcessAffinityMask from the current process to set the affinity of the current process? Or I have to set it up from external tool?

George2 2009-06-27 07:45:34

You can do it from the process itself. It's probably best to start with this MSDN article: http://msdn.microsoft.com/en-us/magazine/cc300701.aspx#S11, it should provide some code as well as helpful background information.

mghie 2009-06-27 07:53:41

I like your reply, about using System.Diagnostics.Process.GetCurrentProcess().ProcessorAffinity property, why should we use IntPrt, why not use int?

George2 2009-06-27 08:19:05

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