Pentium 4 : is smp kernel mandatory ?

Steven Ringwald asric at asric.com
Tue Dec 20 22:02:00 UTC 2005


James Wilkinson wrote:

>Patrick Barnes wrote:
>  
>
>>You are free to uninstall the SMP kernel packages.  Unless you have
>>multiple processors, you'll actually get better performance using the
>>'normal' kernel.  If your processor has 'hyperthreading' or a similar
>>feature, you might want to consider disabling it.  Hyperthreading will
>>look like multiple processors to the kernel, and the SMP kernel will try
>>to take advantage of it, but this will actually usually result in a
>>small performance hit, depending upon how you use your system.  Without
>>the SMP kernel, you will get no benefit at all from the hyperthreading
>>technology.
>>    
>>
>
>I'd be interested to hear what you base this on.
>
>As I understand it, performance with or without hyperthreading on a
>Pentium 4 depends on what you're doing to it and (to an extent) the age
>of the system (it took Intel a while to really tune hyperthreading).
>
>But hyperthreading is supposed to speed up a system, and often does.
>
>Many people have reported interactivity benefits (the system responds to
>interaction faster) even without seeing a total throughput benefit. So
>for example, compressing a number of sound files while watching a video
>might take the same time with or without hyperthreading, but (for
>example) screen updates might be faster with hyperthreading.
>
>Some sites that back my position:
>http://www.2cpu.com/articles/41_1.html
>http://www.anandtech.com/linux/showdoc.aspx?i=2213&p=5
>

 From my experience, also, the smp kernels have APIC interrupts enabled, 
whereas the standard uni-processor ones do not. This is especially 
useful if you have a few cards that need to have interrupts serviced 
frequently, like disk controllers/ethernet controllers, etc. I have one 
system that when it is running in XT-PIC mode ( cat /proc/interrupts ) 
runs like a dog (ok... a dachshund) , but with APIC turned on, runs more 
like a greyhound.

Steve




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