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SubjectIO-APIC in non-SMP mode ?


I am using a SMP board but I have only 1 CPU inserted. So I have an
IO-APIC on-board but I am not running my kernel in SMP mode. Right now my
kernel is not making use of the IO-APIC.

My understanding is that the IO-APIC allows to schedule interrupts to
different processors (which I don't need), but is also a lot faster than
the XT-PIC, thus allowing for much faster handling of interrupts. Is this
correct ?

I tried manually inserting CONFIG_X86_IO_APIC=y and
CONFIG_X86_LOCAL_APIC=y in my .config file and recompiling the kernel just
to see if it boots, but this highly scientific approach must be flawed
because it does not compile anyway :) To be more precise, compilation
fails because FIX_IO_APIC_BASE is undefined, struct mpc_config_intsrc is
undefined, boot_cpu_id is undefined and cpu_present_map is undefined.

Would there be any speed advantage to changing the SMP option to be
YES, NO, or "Uniprocessor on SMP board" with this third option enabling
the IO-APIC ?

Michel "Walken" LESPINASSE - Development Engineer at Wind River Systems -
Microsoft has a Y2K problem. It's called Linux.

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