Re: Linux 2.2.6 IO-APIC <feature>

Ingo Molnar (
Wed, 28 Apr 1999 07:59:41 +0200 (CEST)

On Tue, 27 Apr 1999, Richard B. Johnson wrote:

> Hello IO-APIC/SMP gurus,
> I have finally upgraded all my CPUs to linux 2.2.6. They all work
> except this one! This one refuses to use IRQ0 on both CPUs. The
> kernel declares that the timer is not connected to the APIC. However,
> Linux version 2.1.127 (the last version running on that machine)
> found and used the timer without any problem!
> Perhaps there still needs to be some work done here?
> 0: 54716 0 XT-PIC timer

i would not be worried too much about the timer interrupt. It only does
timekeeping. even in 2.1.127 it was not 'perfect' IO-APIC interrupt, but a
special 'ExtINT' interrupt, delivered to all CPUs. This proved to give
problems on certain boxes. Moving timer-list handling from IRQ0 to the
local per-CPU interrupt in 2.3 should solve this problem. (then IRQ0 will
only be used for timekeeping) [the timer IRQ does not execute the timer
lists, but it's the IRQ mostly likely to trigger timer_bh processing)

if you want to experiment wether your system is able to distribute all
ExtINT interrupts to all CPUs, just change setup_ExtINT_pin() in

- entry.dest.physical.physical_dest = boot_cpu_id;
+ entry.dest.physical.physical_dest = 0xff;

-- mingo

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