Very Computer

I have a box that 4 CPUs that barfs unless I use noapic on the kernel cmd
line.

What are the implications of using this arg?
Is there any loss of functionality/speed?

Thanks, Bruce.

On Wed, 21 Aug 2002 15:17:12 -0700, bruce edge

I can't tell you for sure, but I just finished a kernel build earlier
today, and I'm pretty sure apic is only for uniprocessor systems, so you
really don't want it.

probably not true, from the kernel helptexts:

Local APIC Support on Uniprocessors
CONFIG_X86_UP_APIC
  A local APIC (Advanced Programmable Interrupt Controller) is an
  integrated interrupt controller in the CPU. If you have a single-CPU
  system which has a processor with a local APIC, you can say Y here to
  enable and use it. If you say Y here even though your machine doesn't
  have a local APIC, then the kernel will still run with no slowdown at
  all. The local APIC supports CPU-generated self-interrupts (timer,
  performance counters), and the NMI watchdog which detects hard lockups.

  If you have a system with several CPUs, you do not need to say Y
  here: the local APIC will be used automatically.

And thats why you have to disable it if it does not work.
And that is not good on a SMP box.

kirth

There are two types of APIC - the local APIC, which is on-chip and is
present in most modern x86 systems, and IO-APICs, which are most
commonly found on SMP motherboards. The "noapic" option, iirc, affects
the use of the IO-APIC, and will mean all interrupts are processed on
CPU#0. But these things are super-complicated, so there's undoubtedly
more to it than that.

regards
john