Pentium 4 : is smp kernel mandatory ?

James Wilkinson fedora at
Tue Dec 20 23:08:34 UTC 2005

Steven Ringwald wrote:
> 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.

Couple of points:
 * I'm on x86_64, where APICs are presumed reliable and the default even
   on single-processor systems.

 * Dave Jones says that:
   [Uniprocessor APIC] makes certain laptops (and a few desktops) not
   boot. At all. The only safe way this can be enabled is with a patch
   similar to what is in rawhide kernels right now (With it enabled, but
   off by default [boot with 'lapic' to enable it]), though even that
   still needs work on some boxes.

That's fairly recent. I don't think the patch has got into FC4 updates
yet, but it might be coming. And may well be there on FC5 anyway.

Hope this helps,


E-mail address: james | The opinions expressed herein are not necessarily  | those of my employer, are not necessarily mine, and in
                      | fact are probably not necessary at all...

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