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Old 02-13-2006, 09:57 PM   #1
MamaWombat
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Any advice on disabling hyperthreading and the smp kernel?


Hi all,
I have a Pentium 4 x86_64 with hyperthreading.
I'm using Suse 10.0 with the 2.6.13-15.8-smp kernel.
I also have an nVidia FX3400 graphics card.

Now, I just got some software that highly recommends disabling hyperthreading for best performance.

I know I can disable HT in the BIOS but my concern is with the kernel.
I believe the SMP kernel is for dual processors or hyperthreading... How will it behave if I disable HT?
Will I need to get a new kernel?
Will I need to reinstall the nVidia driver or any other driver?
Can I have the option to switch between no HT and HT?

This is all very confusing for me so any help would be much appreciated.
 
Old 02-13-2006, 10:27 PM   #2
duffmckagan
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SMP refers to "Symmetric Multi-Processing Support".

And this feature (of the kernel) is to be used to processors with Hyperthreading.
If you don't use this feature, you won't use the "Hyperthreading" feature of the processor. I think you may want to use it, since you have paid for it. ;-)

And what about Pentium 4 x86_64?
Is it Itanium?
 
Old 02-13-2006, 11:07 PM   #3
MamaWombat
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Thanks for the quick reply...

So there is no problem using the SMP kernel without hyperthreading?

It's odd that a computationally intensive piece of software like the one I'm trying to use (Nastran finite element solver) can't handle hyper threading! You'd think it would be happy with the extra computing power...

I read up on the difference between the two 64-bit architectures... it's very interesting, apparently nobody uses the Intel 64 bit very much because it's so expensive, and the AMD x86_64, which is just an extension of the good old x86 architecture to 64 bits, works well and is much cheaper, so it is supported by many applications while the IA64 is not. So Intel went and made a chip that copies the chip that AMD copied from them. Or something. And that's how Intel has an x86_64.
It's all rather confusing and I wish things would just work!! But I'm learning the hard way that things often require a lot of work on the user's part!
 
Old 02-13-2006, 11:09 PM   #4
KimVette
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Add one of these as an argument to your kernel:

`nosmp'

or

`maxcpus=1'

To disable SMP support, which will in turn disable ht support.

Then, benchmark the application in question.

If you see an improvement when disabling SMP then you might want to recompile the kernel with SMP disabled - it will save a (miniscule) bit of memory to compile without SMP support.
 
Old 02-13-2006, 11:33 PM   #5
MamaWombat
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and the graphics card drivers?

Cool, thanks for the help.

I gather there will be no problems with the graphics card and other hardware that might be configured to use the HT at the moment?
 
Old 02-13-2006, 11:49 PM   #6
KimVette
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They should still run fine. Some threaded apps might run slightly slower.
 
Old 02-14-2006, 12:02 AM   #7
devinnull
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Quote:
Originally Posted by MamaWombat
It's odd that a computationally intensive piece of software like the one I'm trying to use (Nastran finite element solver) can't handle hyper threading! You'd think it would be happy with the extra computing power...
Keep in mind that hyper threading isn't more hourse power per se. It's a virtual thread that can be used for a 2nd process if the first one is not using all of the CPU. It let's your PC start another task before the first one is finished but it doesn't give you more horse power. With apps that would normaly need most of a processor you may not see much gain from HT.

As to your smp question...looks like other have you taken care of already.
 
  


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